Debugger Tutorial

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# Debugger Tutorial

This tutorial introduces the basic features of the debugger and discusses different debugging methods. It takes you through a simple scenario that demonstrates how the debugger can be used to analyze runtime errors and control program execution.

It is important that you work through Sessions 1 to 5 in sequence.

Notes:

1. For ease of use, the tutorial primarily quotes direct commands to demonstrate the debugger features and not the alternative menu functions.
2. For a full description of all debugger features mentioned in this tutorial, refer to the relevant sections in the remainder of the Debugger documentation.

- Prerequisites

- Fundamentals of Debugging

- Session 1 - Analyzing a Natural Error

- Session 2 - Using a Breakpoint

- Session 3 - Using a Watchpoint

- Session 4 - Tracing the Logical Flow of Programs

- Session 5 - Using Statistics about the Program Execution

- Additional Hints for Using the Debugger

- Example Sources

## Prerequisites

- You should be familiar with programming in Natural.

- Before you start with Session 1, you need to create all example programs (DEBUG1P and DEBUG2P) and subprograms (`DEBUG1N`, `DEBUG2N`, `DEBUG3N` and `DEBUG4N`) provided in the section Example Sources later in this tutorial. Save and catalog these objects with the system command `STOW`.

## Fundamentals of Debugging

The debugger can be used to interrupt the execution flow of a Natural object at a particular debug event and obtain information on the current status of the interrupted object such as the next statement to be executed, the value of a variable and the hierarchy (program levels) of objects called.

You basically need to take the following two major steps to pass control to the debugger for program interruption:

1. Activate the debugger with the system command `TEST ON`.

   This allows the debugger to receive control for each statement to be executed by the Natural runtime system.

2. Set one or more debug entries (breakpoints and watchpoints) for the Natural objects to be executed.

   This allows the debugger to decide when to take over control from the Natural runtime system and interrupt the program execution.

   A Natural error always interrupts the program execution. No debug entry is required then, the debugger steps in automatically.

The following is an overview of all possible program interruptions:

Program Interruption | Explanation
--- | ---
Breakpoint | Causes a program interruption for a statement line in a Natural object. The debugger interrupts the program execution whenever the statement line for which a breakpoint is set is to be executed, that is, before the statement contained in this line is processed.
Watchpoint | Causes a program interruption for a variable in a Natural object. The debugger interrupts the program execution whenever the contents of the variable for which a watchpoint is set have changed, that is, after the statement that references this variable is processed.
Step mode | Steps through the object during the program execution. Step mode is initiated by a debugger command and requires that the debugger previously received control because of a breakpoint or a watchpoint. In step mode, the debugger interrupts the program execution before each executable statement contained in this object is processed.
Natural error | Causes an automatic program interruption.

## Session 1 - Analyzing a Natural Error

This session describes investigation methods for a Natural error that occurs during program execution.

To simulate a Natural error

1. From the `NEXT` prompt, execute `DEBUG1P`.

   The following Natural error message appears: `DEBUG1N 0180 NAT0954 Abnormal termination S0C7 during program execution.`

   The message points to line 180 in the subprogram `DEBUG1N`: `BONUS := SALARY * PERCENT / 100`. This indicates that incorrect values are returned for one or more of the variables referenced. However, at this point, this is no clear evidence of what actually causes the problem; and it could be difficult to determine the cause if the variable values were retrieved from a database (as is typical for employee records).

To activate the debugger for further problem investigation

1. At the `NEXT` prompt, enter the following:

       TEST ON

   The message `Test mode started.` indicates that the debugger is activated.

   Note
   `TEST ON` remains active for the duration of the current session or until you enter `TEST OFF` to deactivate the debugger.

2. Again, execute `DEBUG1P` from the `NEXT` prompt.

   A Debug Break window similar to the example below appears:

       +------------------- Debug Break -------------------+
       | Break by ABEND S0C7 at NATARI2+2A4-4 (NAT0954)    |
       | at line  180 in subprogram DEBUG1N (level 2)      |
       | in library DEBUG    in system file (10,32).       |
       |                                                   |
       |         G   Go                                    |
       |         L   List break                            |
       |         M   Debug Main Menu                       |
       |         N   Next break command                    |
       |         R   Run (set test mode OFF)               |
       |         S   Step mode                             |
       |         V   Variable maintenance                  |
       |                                                   |
       | Code .. G                                         |
       |                                                   |
       | Abnormal termination S0C7 during program execution|
       | PF2=Step,PF13=Next,PF14=Go,PF15=Menu,PF17=SkipS   |
       +---------------------------------------------------+

   Since a Natural error occurs, the debugger steps in automatically and displays the Debug Break window.

   Additional information on where the error occurs is displayed at the top of the window: the module (`NATARI2`) in the Natural nucleus (helpful for support), the type of object (`subprogram`) the library (`DEBUG`) and the database ID and file number (`10,32`) of the system file.

   The Debug Break window also provides debugger functions that can be used, for example, to continue the program execution (Go or Run), invoke the debugger maintenance menu (Debug Main Menu) or activate step mode. You execute a function by using either the appropriate function code or PF key.

To inspect the erroneous statement line

1. In the Code field, replace the default entry `G` by `L` to execute the List break function.

   The source of `DEBUG1N` is displayed:

       13:48:54              ***** NATURAL TEST UTILITIES *****             2007-09-06
       Test Mode ON                - List Object Source -              Object DEBUG1N
                                                                        Bottom of data
       Co Line Source                                                    Message
       __ 0070   2 NUMCHILD  (N2)                                      |
       __ 0080   2 ENTRYDATE (D)                                       |
       __ 0090   2 SALARY    (P7.2)                                    |
       __ 0100   2 BONUS     (P7.2)                                    |
       __ 0110 LOCAL                                                   |
       __ 0120 1 TARGETDATE  (D)    INIT <D'2009-01-01'>               |
       __ 0130 1 DIFFERENCE  (P3.2)                                    |
       __ 0140 1 PERCENT     (P2.2) INIT <3.5>                         |
       __ 0150 END-DEFINE                                              |
       __ 0160 DIFFERENCE := (TARGETDATE - ENTRYDATE) / 365            |
       __ 0170 IF DIFFERENCE GE 10        /* BONUS FOR YEARS IN COMPAN | last line
       __ 0180   BONUS := SALARY * PERCENT / 100                       | * NAT0954 *
       __ 0190 END-IF                                                  |
       __ 0200 SALARY := SALARY + 1800    /* SALARY PLUS ANNUAL INCREA |
       __ 0210 END                                                     |

       Command ===>

       Enter-PF1---PF2---PF3---PF4---PF5---PF6---PF7---PF8---PF9---PF10--PF11--PF12---
             Help  Step  Exit  Last  Scan  Flip  -     +     Li Br <     >     Canc

   `last line` indicates that the statement contained in line 170 is the last statement that executed successfully.

   The statement in line 180 which causes the problem is highlighted and annotated with `* NAT0954 *`.

   This indicates that the error is caused by either the contents of the variable `SALARY` or `PERCENT`. Most likely, this is `SALARY` since `PERCENT` is properly initialized.

To check the contents of `SALARY`

1. In the Command line, enter the following:

       DIS VAR SALARY

   A Display Variable screen similar to the example below appears for the variable `SALARY`:

       18:59:51              ***** NATURAL TEST UTILITIES *****             2007-09-06
       Test Mode ON          - Display Variable (Alphanumeric) -       Object DEBUG1N

       Name ...... EMPLOYEE.SALARY
       Fmt/Len ... P 7.2
       Type ...... parameter
       Index .....
       Range .....

       Position ..
       Contents ..

       Command ===>

       Variable contains invalid data.

       Enter-PF1---PF2---PF3---PF4---PF5---PF6---PF7---PF8---PF9---PF10--PF11--PF12---
             Help  Step  Exit  Last  Mod   Flip              Li Br Alpha Hex   Canc

   The message `Variable contains invalid data.` indicates that the contents of the variable, which seems to be blank, does not match the format of the variable. This becomes clear when you view the hexadecimal representation of the variable contents as described in the next step.

2. Press PF11 (Hex) to display the hexadecimal contents of the variable.

   The screen now looks similar to the example below:

       11:13:33              ***** NATURAL TEST UTILITIES *****             2007-09-06
       Test Mode ON          - Display Variable (Hexadecimal) -        Object DEBUG1N

       Name ...... EMPLOYEE.SALARY
       Fmt/Len ... P 7.2
       Type ...... parameter
       Index .....
       Range .....

       Position ..
       Contents .. 4040404040

       Command ===>

       Enter-PF1---PF2---PF3---PF4---PF5---PF6---PF7---PF8---PF9---PF10--PF11--PF12---
             Help  Step  Exit  Last  Mod   Flip              Li Br Alpha Hex   Canc

   The hexadecimal value shows that the variable is not in packed numeric format, thus leading to a calculation error during the program execution. `DEBUG1P` obviously provides `DEBUG1N` with an incorrect value for `SALARY`.

   Tip
   You can press PF10 (Alpha) to switch back to the alphanumeric representation.

3. In the Command line, enter the following:

       GO

   The command `GO` returns control from the debugger to the Natural runtime system, which continues the program execution until the end of the program or the next debug event. In this case, there is no additional debug event and the `NEXT` prompt appears with the known Natural error message.

To correct `SALARY` in the object source

1. Open `DEBUG1P` with the program editor and remove the comment sign (*) entered for `SALARY := 99000`.

2. Save and catalog the program with the system command `STOW`.

3. Execute `DEBUG1P`.

   The debugger does not interrupt the program though `TEST ON` is still set. The program executes successfully and outputs a report:

       Page      1                                                  07-09-06  15:28:06

       EMPLOYEE RECEIVES:   100800.00
           PLUS BONUS OF:     3465.00

       NEXT                                                               LIB=DEBUG

## Session 2 - Using a Breakpoint

You can interrupt the program execution at a specific statement line by setting a breakpoint for this line.

To set a breakpoint for a statement line in `DEBUG1N`

1. At the `NEXT` prompt, enter the following:

       TEST SET BP DEBUG1N 170

   The message `Breakpoint DEBUG1N0170 set at line 170 of object DEBUG1N.` confirms that a breakpoint with the name `DEBUG1N0170` is set for statement line 170 in the `DEBUG1N` subprogram.

   Notes:

   1. A breakpoint can only be set for an executable statement. If you try to set a statement for a non-executable statement, an appropriate error message appears.
   2. A breakpoint is usually only valid during the current Natural session. If required, you can save a breakpoint for future sessions: see Saving Breakpoints and Watchpoints in Additional Hints for Using the Debugger.

2. Execute `DEBUG1P`.

   The debugger now interrupts the program execution at the statement line, where the new breakpoint is set. The Debug Break window appears:

        +------------------- Debug Break -------------------+
        | Break by breakpoint DEBUG1N0170                   |
        | at line  170 in subprogram DEBUG1N (level 2)      |
        | in library DEBUG    in system file (10,32).       |
        |                                                   |
        |         G   Go                                    |
        |         L   List break                            |
        |         M   Debug Main Menu                       |
        |         N   Next break command                    |
        |         R   Run (set test mode OFF)               |
        |         S   Step mode                             |
        |         V   Variable maintenance                  |
        |                                                   |
        | Code .. G                                         |
        |                                                   |
        |                                                   |
        | PF2=Step,PF13=Next,PF14=Go,PF15=Menu,PF17=SkipS   |
        +---------------------------------------------------+

   The window indicates the name of the breakpoint, the corresponding statement line and object and the library that contains the object. It also indicates the operational level of subprogram `DEBUG1N`.

To view the statement indicated in the Debug Break window

- Execute the List break function.

  The source of DEBUG1N is displayed on the List Object Source screen:

      11:36:45              ***** NATURAL TEST UTILITIES *****             2007-09-06
      Test Mode ON                - List Object Source -              Object DEBUG1N
                                                                       Bottom of data
      Co Line Source                                                    Message
      __ 0070   2 NUMCHILD  (N2)                                      |
      __ 0080   2 ENTRYDATE (D)                                       |
      __ 0090   2 SALARY    (P7.2)                                    |
      __ 0100   2 BONUS     (P7.2)                                    |
      __ 0110 LOCAL                                                   |
      __ 0120 1 TARGETDATE  (D)    INIT <D'2009-01-01'>               |
      __ 0130 1 DIFFERENCE  (P3.2)                                    |
      __ 0140 1 PERCENT     (P2.2) INIT <3.5>                         |
      __ 0150 END-DEFINE                                              |
      __ 0160 DIFFERENCE := (TARGETDATE - ENTRYDATE) / 365            | last line
      __ 0170 IF DIFFERENCE GE 10        /* BONUS FOR YEARS IN COMPAN | DEBUG1N0170
      __ 0180   BONUS := SALARY * PERCENT / 100                       |
      __ 0190 END-IF                                                  |
      __ 0200 SALARY := SALARY + 1800    /* SALARY PLUS ANNUAL INCREA |
      __ 0210 END                                                     |

      Command ===>

      Enter-PF1---PF2---PF3---PF4---PF5---PF6---PF7---PF8---PF9---PF10--PF11--PF12---
            Help  Step  Exit  Last  Scan  Flip  -     +     Li Br <     >     Canc

  Statement line 170 indicated in the Debug Break window is highlighted. The Message column indicates the name of the breakpoint (`DEBUG1N0170`) set for this statement line and the last statement line executed (line 160 as indicated by `last line`).
  Remember: A breakpoint interrupts the program execution before the statement for which the breakpoint is set is processed.

  There are several direct commands you can enter on the List Object Source screen to obtain more information on the current object. As an example, you can view all variables as described in the following step.

To display a list of variables contained in `DEBUG1N`

1. In the Command line, enter the following:

       DIS VAR

   A Display Variables screen similar to the example below appears:

       11:06:13              ***** NATURAL TEST UTILITIES *****             2007-09-06
       Test Mode ON         - Display Variables (Alphanumeric) -       Object DEBUG1N
                                                                                   All
       Co Le Variable Name                    F       Leng Contents               Msg.
           1 EMPLOYEE
       __  2 NAME                             A         20 MEIER
       __  2 ENTRYDATE                        D            1989-01-01
       __  2 SALARY                           P        7.2 99000.00
       __  2 BONUS                            P        7.2 *** invalid data ***
       __  1 TARGETDATE                       D            2009-01-01
       __  1 DIFFERENCE                       P        3.2 20.00
       __  1 PERCENT                          P        2.2 3.50

       Command ===>

       Enter-PF1---PF2---PF3---PF4---PF5---PF6---PF7---PF8---PF9---PF10--PF11--PF12---
             Help  Step  Exit  Last  Zoom  Flip  -     +     Li Br Alpha Hex   Canc

   The screen lists all variables defined in `DEBUG1N`. You can neglect the remark `invalid data` for `BONUS`. In this case, it is not essential whether `BONUS` is properly initialized since it is used as a target operand only. However, to exercise another debugger command, change the contents of `BONUS` in the following step.

To check and modify the contents of `BONUS`

1. In the Co column, next to `BONUS`, enter the following:

       MO

   Or:
   In the Command line, enter the following:

       MOD VAR BONUS

   A Modify Variable screen similar to the example below appears:

       11:29:50              ***** NATURAL TEST UTILITIES *****             2007-09-06
       Test Mode ON          - Modify Variable (Alphanumeric) -        Object DEBUG1N

       Name ...... EMPLOYEE.BONUS
       Fmt/Len ... P 7.2
       Type ...... parameter
       Index .....
       Range .....

       Position .. 1
       Contents .. ___________

       Command ===>

       Variable contains invalid data.

       Enter-PF1---PF2---PF3---PF4---PF5---PF6---PF7---PF8---PF9---PF10--PF11--PF12---
             Help  Step  Exit  Last  Save  Flip              Li Br Alpha Hex   Canc

2. You can use the hexadecimal display to verify that the variable is not in packed numeric format. Press PF10 (Alpha) to switch back to the alphanumeric representation.

3. In the Contents field, enter a value in packed numeric format, for example, `12345.00` and press PF5 (Save).

   The screen now looks similar to the example below:

       11:50:00              ***** NATURAL TEST UTILITIES *****             2007-09-06
       Test Mode ON          - Display Variable (Alphanumeric) -       Object DEBUG1N

       Name ...... EMPLOYEE.BONUS
       Fmt/Len ... P 7.2
       Type ...... parameter
       Index .....
       Range .....

       Position ..
       Contents .. 12345.00

       Command ===>

       Variable BONUS modified.

       Enter-PF1---PF2---PF3---PF4---PF5---PF6---PF7---PF8---PF9---PF10--PF11--PF12---
             Help  Step  Exit  Last  Mod   Flip              Li Br Alpha Hex   Canc

   A message confirms the modification of Contents.

4. Press PF9 (Li Br) or PF3 (Exit).

   The List Object Source screen appears.

5. In the Command line, enter the following:

       GO

   The debugger returns control to the Natural runtime system, which finishes executing DEBUG1P since no further debug event occurs. The report produced by the program is output:

       Page      1                                                  07-09-06  10:02:51

       EMPLOYEE RECEIVES:   100800.00
           PLUS BONUS OF:     3465.00

       NEXT                                                               LIB=DEBUG

6. Before you continue with the next session, delete all current breakpoints by entering the following at the NEXT prompt:

       TEST DEL BP * *

   A message appears confirming that all breakpoint (in this case, only one breakpoint) are deleted.

## Session 3 - Using a Watchpoint

`DEBUG1P` and `DEBUG1N` perform a calculation for a single employee's bonus and salary payment. If multiple employee records were processed, you would probably test whether the variable `BONUS` is now updated correctly. This is done by setting a watchpoint for this variable. A watchpoint allows the debugger to interrupt the program execution when the contents of the specified variable change.

To set a watchpoint for the variable `BONUS`

1. At the NEXT prompt, enter the following:

       TEST SET WP DEBUG1N BONUS

   The message `Watchpoint BONUS set for variable EMPLOYEE.BONUS.` confirms that a watchpoint is set for the variable `BONUS` in the `DEBUG1N` example subprogram.

   Notes:

   1. If you enter a debugger direct command in the Command line of a debugger screen, you must omit the keyword `TEST`. For example, instead of `TEST SET WP DEBUG1N BONUS`, you would then enter `SET WP DEBUG1N BONUS` only.
   2. A watchpoint is usually only valid during the current Natural session. If required, you can save a watchpoint for future sessions: see Saving Breakpoints and Watchpoints in Additional Hints for Using the Debugger.

2. Execute `DEBUG1P` from the `NEXT` prompt.

   The debugger interrupts the program execution at the new watchpoint and invokes the Debug Break window:

       +------------------- Debug Break -------------------+
       | Break by watchpoint BONUS                         |
       | at line  180 in subprogram DEBUG1N (level 2)      |
       | in library DEBUG    in system file (10,32).       |
       |                                                   |
       |         G   Go                                    |
       |         L   List break                            |
       |         M   Debug Main Menu                       |
       |         N   Next break command                    |
       |         R   Run (set test mode OFF)               |
       |         S   Step mode                             |
       |         V   Variable maintenance                  |
       |                                                   |
       | Code .. G                                         |
       |                                                   |
       |                                                   |
       | PF2=Step,PF13=Next,PF14=Go,PF15=Menu,PF17=SkipS   |
       +---------------------------------------------------+

   The window indicates that a watchpoint was detected in line 180. This line contains the statement that processes the variable `BONUS`.

   The debugger interrupted the program execution after the statement for `BONUS` was processed. Only then could the debugger recognize that the contents of the variable had changed.

3. Execute the List break function.

   The List Object Source now looks similar to the example below:

       16:24:46              ***** NATURAL TEST UTILITIES *****             2007-09-06
       Test Mode ON                - List Object Source -              Object DEBUG1N
                                                                        Bottom of data
       Co Line Source                                                    Message
       __ 0070   2 NUMCHILD  (N2)                                      |
       __ 0080   2 ENTRYDATE (D)                                       |
       __ 0090   2 SALARY    (P7.2)                                    |
       __ 0100   2 BONUS     (P7.2)                                    |
       __ 0110 LOCAL                                                   |
       __ 0120 1 TARGETDATE  (D)    INIT <D'2009-01-01'>               |
       __ 0130 1 DIFFERENCE  (P3.2)                                    |
       __ 0140 1 PERCENT     (P2.2) INIT <3.5>                         |
       __ 0150 END-DEFINE                                              |
       __ 0160 DIFFERENCE := (TARGETDATE - ENTRYDATE) / 365            |
       __ 0170 IF DIFFERENCE GE 10        /* BONUS FOR YEARS IN COMPAN | DEBUG1N0170
       __ 0180   BONUS := SALARY * PERCENT / 100                       | BONUS
       __ 0190 END-IF                                                  |
       __ 0200 SALARY := SALARY + 1800    /* SALARY PLUS ANNUAL INCREA |
       __ 0210 END                                                     |

       Command ===>

       Enter-PF1---PF2---PF3---PF4---PF5---PF6---PF7---PF8---PF9---PF10--PF11--PF12---
             Help  Step  Exit  Last  Scan  Flip  -     +     Li Br <     >     Canc

   The statement which references the variable `BONUS` is highlighted and the Message column indicates the name of the watchpoint set for the variable.

To check for changes in `BONUS`

1. In the Command line, enter the following:

       DIS VAR BONUS

   The Display Variable screen appears and displays a value of `3465.00` in the Contents field. This shows that the contents of the variable `BONUS` have changed.

2. Press PF3 (Exit) to return to the List Object Source screen.

To check for changes in `SALARY`

1. To test the contents of the variable `SALARY` in a later step, set a breakpoint for `SALARY` by entering the following in the Co column of line 200:

       SE

   From the List Object Source screen, a line command such as `SE` is a convenient alternative to using the `SET BP` direct command.

   The Message column indicates that a breakpoint (`BP`) is set for line 200:

       17:55:58              ***** NATURAL TEST UTILITIES *****             2007-09-06
       Test Mode ON                - List Object Source -              Object DEBUG1N
                                                                        Bottom of data
       Co Line Source                                                    Message
       __ 0070   2 NUMCHILD  (N2)                                      |
       __ 0080   2 ENTRYDATE (D)                                       |
       __ 0090   2 SALARY    (P7.2)                                    |
       __ 0100   2 BONUS     (P7.2)                                    |
       __ 0110 LOCAL                                                   |
       __ 0120 1 TARGETDATE  (D)    INIT <D'2009-01-01'>               |
       __ 0130 1 DIFFERENCE  (P3.2)                                    |
       __ 0140 1 PERCENT     (P2.2) INIT <3.5>                         |
       __ 0150 END-DEFINE                                              |
       __ 0160 DIFFERENCE := (TARGETDATE - ENTRYDATE) / 365            |
       __ 0170 IF DIFFERENCE GE 10        /* BONUS FOR YEARS IN COMPAN | DEBUG1N0170
       __ 0180   BONUS := SALARY * PERCENT / 100                       | BONUS
       __ 0190 END-IF                                                  |
       __ 0200 SALARY := SALARY + 1800    /* SALARY PLUS ANNUAL INCREA | BP set
       __ 0210 END                                                     |

       Command ===>

       Enter-PF1---PF2---PF3---PF4---PF5---PF6---PF7---PF8---PF9---PF10--PF11--PF12---
             Help  Step  Exit  Last  Scan  Flip  -     +     Li Br <     >     Canc

2. In the Command line, enter the following:

       GO

   The Debug Break window appears:

       +------------------- Debug Break -------------------+
       | Break by breakpoint DEBUG1N0200                   |
       | at line  200 in subprogram DEBUG1N (level 2)      |
       | in library DEBUG    in system file (10,32).       |
       |                                                   |
       |         G   Go                                    |
       |         L   List break                            |
       |         M   Debug Main Menu                       |
       |         N   Next break command                    |
       |         R   Run (set test mode OFF)               |
       |         S   Step mode                             |
       |         V   Variable maintenance                  |
       |                                                   |
       | Code .. G                                         |
       |                                                   |
       |                                                   |
       | PF2=Step,PF13=Next,PF14=Go,PF15=Menu,PF17=SkipS   |
       +---------------------------------------------------+

3. Execute the List break function.

   The List Object Source screen now looks similar to the example below:

       10:49:31              ***** NATURAL TEST UTILITIES *****             2007-09-06
       Test Mode ON                - List Object Source -              Object DEBUG1N
                                                                        Bottom of data
       Co Line Source                                                    Message
       __ 0070   2 NUMCHILD  (N2)                                      |
       __ 0080   2 ENTRYDATE (D)                                       |
       __ 0090   2 SALARY    (P7.2)                                    |
       __ 0100   2 BONUS     (P7.2)                                    |
       __ 0110 LOCAL                                                   |
       __ 0120 1 TARGETDATE  (D)    INIT <D'2009-01-01'>               |
       __ 0130 1 DIFFERENCE  (P3.2)                                    |
       __ 0140 1 PERCENT     (P2.2) INIT <3.5>                         |
       __ 0150 END-DEFINE                                              |
       __ 0160 DIFFERENCE := (TARGETDATE - ENTRYDATE) / 365            |
       __ 0170 IF DIFFERENCE GE 10        /* BONUS FOR YEARS IN COMPAN | DEBUG1N0170
       __ 0180   BONUS := SALARY * PERCENT / 100                       | last line
       __ 0190 END-IF                                                  |
       __ 0200 SALARY := SALARY + 1800    /* SALARY PLUS ANNUAL INCREA | DEBUG1N0200
       __ 0210 END                                                     |

       Command ===>

       Enter-PF1---PF2---PF3---PF4---PF5---PF6---PF7---PF8---PF9---PF10--PF11--PF12---
             Help  Step  Exit  Last  Scan  Flip  -     +     Li Br <     >     Canc

   Since this is a breakpoint, the statement that references (and updates) `SALARY` has not yet been executed. As a result, the contents of the variable have not changed.

4. In the Command line, enter `DIS VAR SALARY` to verify that the contents of `SALARY` are unchanged.

   The variable screen proves that `SALARY` still contains `99000`, the initial value assigned in `DEBUG1P`.

5. To view the update of the variable contents, step to the next statement by choosing either of the following methods:

   In the Command line, enter the following:

       STEP

   Or:
   Press PF2 (Step).

   The screen now looks similar to the example below:

       13:38:24              ***** NATURAL TEST UTILITIES *****             2007-09-06
       Test Mode ON                - List Object Source -              Object DEBUG1N
                                                                        Bottom of data
       Co Line Source                                                    Message
       __ 0070   2 NUMCHILD  (N2)                                      |
       __ 0080   2 ENTRYDATE (D)                                       |
       __ 0090   2 SALARY    (P7.2)                                    |
       __ 0100   2 BONUS     (P7.2)                                    |
       __ 0110 LOCAL                                                   |
       __ 0120 1 TARGETDATE  (D)    INIT <D'2009-01-01'>               |
       __ 0130 1 DIFFERENCE  (P3.2)                                    |
       __ 0140 1 PERCENT     (P2.2) INIT <3.5>                         |
       __ 0150 END-DEFINE                                              |
       __ 0160 DIFFERENCE := (TARGETDATE - ENTRYDATE) / 365            |
       __ 0170 IF DIFFERENCE GE 10        /* BONUS FOR YEARS IN COMPAN | DEBUG1N0170
       __ 0180   BONUS := SALARY * PERCENT / 100                       |
       __ 0190 END-IF                                                  |
       __ 0200 SALARY := SALARY + 1800    /* SALARY PLUS ANNUAL INCREA | last line
       __ 0210 END                                                     | step mode

       Command ===>

       Enter-PF1---PF2---PF3---PF4---PF5---PF6---PF7---PF8---PF9---PF10--PF11--PF12---
             Help  Step  Exit  Last  Scan  Flip  -     +     Li Br <     >     Canc

   You skipped one line and processed the next executable statement in line 200, which updates `SALARY`. The Message column indicates that step mode is set. In step mode, the debugger continues the program execution at the next executable statement.

6. In the Command line, enter `DIS VAR SALARY` to check the variable contents.

   The Display Variable screen appears and displays a value of `100800.00` in the Contents field. This proves that the contents of the variable `SALARY` have changed.

7. In the Command line, enter the following:

       GO

   The debugger returns control to the Natural runtime system, which finishes executing `DEBUG1P` since no further debug event occurs. The report produced by the program is output.

## Session 4 - Tracing the Logical Flow of Programs

This session describes debugging methods you can use to better understand, overview and control a complex Natural application with numerous objects.

The session starts out with instructions for analyzing the logical flow of an application on the statement level. It then demonstrates how breakpoints can be used to find out the sequence in which programs are executed.

The instructions in this session are based on a simple (but sufficient for demonstration) example application that consists of one program (`DEBUG2P`) and three subprograms (`DEBUG2N`, `DEBUG3N` and `DEBUG4N`).

To set a breakpoint at program begin or end

1. Set a breakpoint for `DEBUG2P` by entering the following at the `NEXT` prompt:

       TEST SET BP DEBUG2P BEG

   The message `Breakpoint DEBUG2P-BEG set at line BEG of object DEBUG2P.` confirms that a breakpoint is set in `DEBUG2N`.

   Using the keyword `BEG` instead of a specific line number has the effect that the breakpoint is set at the beginning of the program, that is, for the first statement to be executed. This can even be the `DEFINE DATA` statement, for example, if an `INIT` clause is used, which generates an executable statement when the program is cataloged.

   Tip

   You can also specify the keyword `END` to set a breakpoint for the last statement to be executed. This can be the `END` statement but also the `FETCH` or `CALLNAT` statement.

2. Execute `DEBUG2P`.

   The Debug Break window appears:

       +------------------- Debug Break -------------------+
       | Break by breakpoint DEBUG2P-BEG                   |
       | at line  130 in program DEBUG2P (level 1)         |
       | in library DEBUG    in system file (10,32).       |
       |                                                   |
       |         G   Go                                    |
       |         L   List break                            |
       |         M   Debug Main Menu                       |
       |         N   Next break command                    |
       |         R   Run (set test mode OFF)               |
       |         S   Step mode                             |
       |         V   Variable maintenance                  |
       |                                                   |
       | Code .. G                                         |
       |                                                   |
       |                                                   |
       | PF2=Step,PF13=Next,PF14=Go,PF15=Menu,PF17=SkipS   |
       +---------------------------------------------------+

   The debugger now steps in at the first breakpoint set for the program.

3. Execute the List break function to check the source and see that the debugger now steps in at the first executable statement `NAME := 'MEIER'`.

To step through an application

1. On the List Object Source screen, set step mode by either pressing PF2 (Step) or entering `STEP` in the Command line.

   The last statement executed is annotated with `last line`. The next statement to be executed is highlighted and annotated with `step mode`.

   Tip

   If you do not want the debugger to pause at every single statement but step through an application more quickly, in the `STEP` command, specify the number of statements you want to skip, for example: `STEP 2` or `STEP 10`.

2. Press PF2 (Step) repeatedly until the `CALLNAT` statement is annotated with `step mode`.

3. Continue with PF2 (Step) and execute the `CALLNAT`.

   The invoked subprogram `DEBUG2N` is displayed, where the next statement to be executed is highlighted:

       11:59:19              ***** NATURAL TEST UTILITIES *****             2007-09-06
       Test Mode ON                - List Object Source -              Object DEBUG2N
                                                                           Top of data
       Co Line Source                                                    Message
       __ 0010 ** SUBPROGRAM DEBUG2N: CALLS 'DEBUG3N' AND 'DEBUG4N'FOR |
       __ 0020 ******************************************************* |
       __ 0030 DEFINE DATA                                             | step mode
       __ 0040 PARAMETER                                               |
       __ 0050 1 EMPLOYEE                                              |
       __ 0060   2 NAME      (A20)                                     |
       __ 0070   2 NUMCHILD  (N2)                                      |
       __ 0080   2 ENTRYDATE (D)                                       |
       __ 0090   2 SALARY    (P7.2)                                    |
       __ 0100   2 BONUS     (P7.2)                                    |
       __ 0110 LOCAL                                                   |
       __ 0120 1 TARGETDATE  (D)    INIT <D'2009-01-01'>               |
       __ 0130 1 DIFFERENCE  (P3.2)                                    |
       __ 0140 1 PERCENT     (P2.2) INIT <3.5>                         |
       __ 0150 END-DEFINE                                              |

       Command ===>

       Enter-PF1---PF2---PF3---PF4---PF5---PF6---PF7---PF8---PF9---PF10--PF11--PF12---
             Help  Step  Exit  Last  Scan  Flip  -     +     Li Br <     >     Canc

   As an alternative, you could skip the `CALLNAT` by entering `STEP SKIP` in the Command line.

   You would then only step through the statements in the invoking program `DEBUG2` but not through the statements within an invoked subprogram.

To view the levels at which the objects are executed

1. In the List Object Source screen of `DEBUG2N`, enter the following in the Command line:

       OBJCHAIN

   A Break Information screen similar to the example below appears:

       13:45:34               ***** NATURAL TEST UTILITIES *****            2007-09-06
                                    - Break Information -

       No GDA active for the current program.

       Break by step mode
       at line   30 in subprogram DEBUG2N (level 2)
       in library DEBUG    in system file (10,32).

   In addition to the object information already known, this screen indicates whether the program references a GDA (global data area).

2. Press ENTER to scroll down one page.

   The screen now looks similar to the example below:

       13:46:34               ***** NATURAL TEST UTILITIES *****            2007-09-06
                                  - Current Object Chain -

       Level Name     Type        Line Library   DBID   FNR
         2   DEBUG2N  Subprogram     0 DEBUG       10    32
         1   DEBUG2P  Program      170 DEBUG       10    32

   This screen indicates the operational levels at which the objects are executed: subprogram `DEBUG2N` is executed at level 2 and program `DEBUG2P` (which invokes the subprogram) is executed at the superior level 1.

3. Press ENTER.

   The List Object Source screen appears.

4. In the Command line, enter the following:

       GO

   The debugger returns control to the Natural runtime system, which finishes executing `DEBUG2P` since no further debug event occurs. The report produced by the program is output:

       Page      1                                                  07-09-06  10:04:21

       EMPLOYEE RECEIVES:    99300.00
           PLUS BONUS OF:     3565.00

       NEXT                                                               LIB=DEBUG

5. Delete all breakpoints currently set by entering the following at the `NEXT` prompt:

       TEST DEL BP * *

   A message appears confirming that all breakpoints are deleted.

To set breakpoints to follow the program execution

1. At the NEXT prompt, enter the following:

       TEST SET BP ALL BEG

   The message `Breakpoint ALL-BEG set at line BEG of object ALL.` appears.

   This indicates that you have set a breakpoint for the first executable statement of each object to be executed.

2. Execute `DEBUG2P`.

   A Debug Break window appears for `DEBUG2P`.

3. Execute the Go function repeatedly.

   Each time you execute Go, the next object invoked is indicated in the Debug Break window (`DEBUG2N` first and then `DEBUG3N` and `DEBUG4N`). Thus, you can easily determine which objects are invoked at what point during the program execution. Additionally, for each object, you can apply the menu functions of the Debug Break window.

4. When the `NEXT` prompt appears, delete all breakpoints currently set by entering the following:

       TEST DEL BP * *

   A message appears confirming that all breakpoints are deleted.

## Session 5 - Using Statistics about the Program Execution

You can use the debugger to view statistical information on which objects are called and how often they are called. Additionally, you can find out which statements are executed, and how often.

To check what objects are called during program execution

1. At the NEXT prompt, enter the following:

       TEST SET CALL ON

   The message `Call statistics started.` confirms that the statistics function is activated.

2. Execute `DEBUG2P`.

   The debugger logs all object calls executed, and the report produced by the program is output.

3. At the `NEXT` prompt, enter the following:

       TEST DIS CALL

   A Display Called Objects screen similar to the example below appears:

       10:43:47              ***** NATURAL TEST UTILITIES *****             2007-09-06
       Test Mode ON              - Display Called Objects -            Object
                                                                                   All
       Object   Library  Type         DBID   FNR S/C Ver Cat Date   Time       Calls
       *_______ DEBUG___
       DEBUG2P  DEBUG    Program        10    32 S/C 4.2 2007-08-30 13:48          1
       DEBUG2N  DEBUG    Subprogram     10    32 S/C 4.2 2007-08-30 13:48          1
       DEBUG3N  DEBUG    Subprogram     10    32 S/C 4.2 2007-08-30 13:48          1
       DEBUG4N  DEBUG    Subprogram     10    32 S/C 4.2 2007-08-30 13:48          1

       Command ===>

       Enter-PF1---PF2---PF3---PF4---PF5---PF6---PF7---PF8---PF9---PF10--PF11--PF12---
             Help        Exit  Last        Flip        +                       Canc

   The screen lists all objects executed: the invoking program (`DEBUG2P`) and all other objects invoked (`DEBUG2N`, `DEBUG3N` and `DEBUG4N`). It also indicates how frequently each object is invoked (`CALLS`), the type of object called, where the object is stored and under which Natural version, whether source and cataloged objects exist, and when the object was cataloged.

4. Press PF3 (Exit) or PF12 (Canc) until the `NEXT` prompt appears.

To check which statements are executed during program execution

1. At the `NEXT` prompt, enter the following:

       TEST SET XSTAT COUNT

   The message `Statement execution counting started for library/object */*.` confirms that the statistics function is activated for all objects contained in the current library and all steplibs concatenated with this library.

2. Execute `DEBUG2P`.

   The debugger logs all statements processed by the program before the report produced by the program is output.

3. At the `NEXT` prompt, enter the following:

       TEST DIS XSTAT

   A List Statement Execution Statistics screen similar to the example below appears:

       11:39:10              ***** NATURAL TEST UTILITIES *****             2007-09-06
       Test Mode ON        - List Statement Execution Statistics -     Object
                                                                                   All
       Co Object   Library  Type        DBID   FNR Obj.Called Exec Exec   %  Total No.
          *_______ *_______                           n Times able uted     Executions
       __ DEBUG2P  DEBUG    Program       10    32          1    8    8 100          8
       __ DEBUG2N  DEBUG    Subprogram    10    32          1    8    8 100          8
       __ DEBUG3N  DEBUG    Subprogram    10    32          1    2    2 100          2
       __ DEBUG4N  DEBUG    Subprogram    10    32          1   10    7  70          7

       Command ===>

       Enter-PF1---PF2---PF3---PF4---PF5---PF6---PF7---PF8---PF9---PF10--PF11--PF12---
             Help        Exit  Last        Flip  -     +                       Canc

   The screen lists the number of calls (`Obj. Called n Times`), the number of executable statements (`Exec able`), the number of executed statements (`Executed`), the percentage of executed statements as related to the total number of executable statements (`%`), and the total number of executed statements (`Total No. Executions`).

4. In the Co column, next to `DEBUG4N`, enter the following:

       DS

   A statistics screen similar to the example below appears:

       12:11:19              ***** NATURAL TEST UTILITIES *****             2007-09-06
       Test Mode ON             - Display Statement Lines -            Object DEBUG4N

       Line Source                                                              Count
       0010 ** SUBPROGRAM 'DEBUG4N': CALCULATES SPECIAL SALARY INCREASE
       0020 ************************************************************
       0030 DEFINE DATA
       0040 PARAMETER
       0050 1 SALARY (P7.2)
       0060 END-DEFINE
       0070 DECIDE FOR FIRST CONDITION                                              1
       0080   WHEN SALARY < 50000                                                   1
       0090     SALARY := SALARY + 1800                                  not executed
       0100   WHEN SALARY < 70000                                                   1
       0110     SALARY := SALARY + 1200                                  not executed
       0120   WHEN SALARY < 90000                                                   1
       0130     SALARY := SALARY + 600                                   not executed
       0140   WHEN NONE                                                             1
       0150     SALARY := SALARY + 300                                              1

       Command ===>

       Enter-PF1---PF2---PF3---PF4---PF5---PF6---PF7---PF8---PF9---PF10--PF11--PF12---
             Help        Exit  Last        Flip        +                       Canc

   The screen indicates how often a statement was executed and the executable statements that were not processed.

## Additional Hints for Using the Debugger

This section provides additional hints for using the debugger.

- Time Stamps of Objects

- Saving Breakpoints and Watchpoints

- Debug Main Menu for Maintenance Functions

- Help for Commands on Maintenance Screens

- Major Functions Available during Program Interruption

- Next Option for Additional Commands During Program Interruption

- Displaying Large Variables and Arrays

- Printing Debugger Statistics

- Using the Debugger in Batch Mode

### Time Stamps of Objects

A cataloged object that does not exactly correspond to the source object can cause debugging errors. If you want to guarantee that source and cataloged object correspond to each other, save and catalog them with the system command `STOW`.

For details, see the section Operational Requirements.

### Saving Breakpoints and Watchpoints

You can save the breakpoints and watchpoints set in the current session as a debug environment and load this environment for use in a future session. This is helpful if you want to repeatedly test an application with the same debug entries.

For details, see the section Debug Environment Maintenance.

### Debug Main Menu for Maintenance Functions

All debugger maintenance functions, such as setting a breakpoint or creating statistics, can be executed by using either a direct command or the maintenance functions provided in the Debug Main Menu. You open this menu by entering one of the following:

- `TEST`
  at a command prompt.

- `MENU`
  at the Command line of a debugger screen.

- `M`
  in the Code field of the Debug Break window.

### Help for Commands on Maintenance Screens

For a list of direct commands available on a debugger maintenance screen, press PF1 (Help) or enter a question mark (?) in the Command line.

A debugger maintenance screen that contains list items usually also provides line commands that can be used to further process an item. You enter a line command in the Co column, next to the required item. For a list of valid line commands, enter a question mark (?) in this column.

### Major Functions Available during Program Interruption

The major functions available during the program interruption are listed in the following section. They can be executed from either the Debug Break window or the Command line of a debugger maintenance screen.

Code in Debug Window | Alternative Direct Command | Function
--- | --- | ---
`G` | `GO` | Continues the program execution until the next debug event occurs.
`L` | `LIST BREAK` | Lists the object source at the statement line where the debug event occurs.
`N` | `NEXT` | Executes the next break command if specified for a breakpoint or watchpoint. See also Next Option for Additional Commands During Program Interruption.
`R` | `RUN` | Switches test mode off and continues the program execution.
`S` | `STEP` | Processes the executable statements line by line.
`V` | `DIS VAR` | Displays a list of variables defined for the interrupted object.

### Next Option for Additional Commands During Program Interruption

When displaying or modifying a breakpoint or watchpoint, you will notice that the debugger command `BREAK` is attached to each of them. This command invokes the Debug Break window and must not be removed. However, you can specify additional debugger commands to be executed during the program interruption after the `BREAK` command. An additional command is executed when you enter either the command `NEXT` in the Command line or the function code `N` in the Debug Break window.

You enter the debugger commands in the Commands field of the appropriate breakpoint or watchpoint maintenance screen as shown in the following example:

    11:38:55              ***** NATURAL TEST UTILITIES *****             2007-09-06
    Test Mode ON                - Modify Breakpoint -               Object

    Spy number ..............   1
    Initial state ........... A (A = Active, I = Inactive)
    Breakpoint name ......... DEBUG1P0170_   DBID/FNR ....... 10/32
    Object name ............. DEBUG1P_       Library ........ DEBUG
    Line number ............. 0170
    Label ................... ________________________________
    Skips before execution .. ____0
    Max number executions ... ____0

    Commands ... BREAK_______________________________________________________
                 STACK_______________________________________________________
                 DIS VAR BONUS_______________________________________________
                 ____________________________________________________________
                 ____________________________________________________________
                 ____________________________________________________________

    Command ===>

    Enter-PF1---PF2---PF3---PF4---PF5---PF6---PF7---PF8---PF9---PF10--PF11--PF12---
          Help        Exit  Last  Save  Flip                                Canc

In the example above, the command `STACK` instructs the debugger to view the Natural stack. The command `DIS VAR BONUS` instructs the debugger to display the specified variable. This is helpful, for example, if you set a breakpoint in a loop and always want to view the value of one particular variable only. You then do not have to enter the `DIS VAR` command repeatedly.

For details, see the description of the field Commands in the sections Fields and Columns on Breakpoint Screens and Fields and Columns on Watchpoint Screens.

### Displaying Large Variables and Arrays

The Display Variable screen shows all definitions of a variable and displays its contents in alphanumeric or hexadecimal format. For the display features available for large variables, whose contents extend beyond the current screen or variables with array definitions, see the section Display Variable - Individual.

### Printing Debugger Statistics

You can print the statistical reports produced by the debugger or download them to a PC.

For details, see Print Objects in the section Call Statistics Maintenance and Print Statements in the section Statement Execution Statistics Maintenance.

### Using the Debugger in Batch Mode

The debugger is mainly designed for interactive operations in online mode. Although you can, in principle, execute all debugger features in batch mode, processing online operations in batch (for example, the use of PF keys) can require complex batch programming. However, there are also debugger features for which batch processing is a convenient alternative. One example is collecting and printing statistical data about an application as described in Example of Generating and Printing Statistics in Batch in the section Batch Processing.

## Example Sources

This section contains the source code of the example programs and subprograms required in Sessions 1 to 5.

#### Program `DEBUG1P`

    ** PROGRAM 'DEBUG1P: CALLS 'DEBUG1N' FOR SALARY AND BONUS CALCULATION
    **********************************************************************
    DEFINE DATA
    LOCAL
    1 EMPLOYEE    (A42)
    1 REDEFINE EMPLOYEE
      2 NAME      (A20)
      2 NUMCHILD  (N2)
      2 ENTRYDATE (D)
      2 SALARY    (P7.2)
      2 BONUS     (P7.2)
    END-DEFINE
    NAME      := 'MEIER'
    NUMCHILD  := 2
    ENTRYDATE := D'1989-01-01'
    * SALARY  := 99000
    CALLNAT 'DEBUG1N' NAME NUMCHILD ENTRYDATE SALARY BONUS
    WRITE 'EMPLOYEE RECEIVES:'   SALARY
    WRITE '    PLUS BONUS OF:'   BONUS
    END

#### Subprogram `DEBUG1N`

    ** SUBPROGRAM 'DEBUG1N': CALCULATES BONUS AND SALARY INCREASE
    ************************************************************************
    DEFINE DATA
    PARAMETER
    1 EMPLOYEE
      2 NAME      (A20)
      2 NUMCHILD  (N2)
      2 ENTRYDATE (D)
      2 SALARY    (P7.2)
      2 BONUS     (P7.2)
    LOCAL
    1 TARGETDATE  (D)    INIT <D'2009-01-01'>
    1 DIFFERENCE  (P3.2)
    1 PERCENT     (P2.2) INIT <3.5>
    END-DEFINE
    DIFFERENCE := (TARGETDATE - ENTRYDATE) / 365
    IF DIFFERENCE GE 10        /* BONUS FOR YEARS IN COMPANY
      BONUS := SALARY * PERCENT / 100
    END-IF
    SALARY := SALARY + 1800    /* SALARY PLUS ANNUAL INCREASE
    END

#### Program `DEBUG2P`

    ** PROGRAM 'DEBUG2P': CALLS 'DEBUG2N'FOR SALARY AND BONUS CALCULATION
    ************************************************************************
    DEFINE DATA
    LOCAL
    1 EMPLOYEE    (A42)
    1 REDEFINE EMPLOYEE
      2 NAME      (A20)
      2 NUMCHILD  (N2)
      2 ENTRYDATE (D)
      2 SALARY    (P7.2)
      2 BONUS     (P7.2)
    END-DEFINE
    NAME      := 'MEIER'
    NUMCHILD  := 2
    ENTRYDATE := D'1989-01-01'
    SALARY    := 99000
    CALLNAT 'DEBUG2N' NAME NUMCHILD ENTRYDATE SALARY BONUS
    WRITE 'EMPLOYEE RECEIVES:'   SALARY
    WRITE '    PLUS BONUS OF:'   BONUS
    END

#### Subprogram `DEBUG2N`

    ** SUBPROGRAM DEBUG2N: CALLS 'DEBUG3N' AND 'DEBUG4N'FOR SPECIAL RATES
    ************************************************************************
    DEFINE DATA
    PARAMETER
    1 EMPLOYEE
      2 NAME      (A20)
      2 NUMCHILD  (N2)
      2 ENTRYDATE (D)
      2 SALARY    (P7.2)
      2 BONUS     (P7.2)
    LOCAL
    1 TARGETDATE  (D)    INIT <D'2009-01-01'>
    1 DIFFERENCE  (P3.2)
    1 PERCENT     (P2.2) INIT <3.5>
    END-DEFINE
    DIFFERENCE := (TARGETDATE - ENTRYDATE) / 365
    IF DIFFERENCE GE 10        /* BONUS FOR YEARS IN COMPANY
      BONUS := SALARY * PERCENT / 100
    END-IF
    IF NUMCHILD > 0
      CALLNAT 'DEBUG3N' NUMCHILD BONUS     /* SPECIAL BONUS
    END-IF
    CALLNAT 'DEBUG4N' SALARY               /* SPECIAL SALARY INCREASE
    END

#### Subprogram `DEBUG3N`

    ** SUBPROGRAM 'DEBUG3N': CALCULATES SPECIAL BONUS
    ************************************************************************
    DEFINE DATA
    PARAMETER
    1 NUMCHILD (N2)
    1 BONUS    (P7.2)
    END-DEFINE
    BONUS := BONUS + NUMCHILD * 50
    END

#### Subprogram `DEBUG4N`

    ** SUBPROGRAM 'DEBUG4N': CALCULATES SPECIAL SALARY INCREASE
    ************************************************************************
    DEFINE DATA
    PARAMETER
    1 SALARY (P7.2)
    END-DEFINE
    DECIDE FOR FIRST CONDITION
      WHEN SALARY < 50000
        SALARY := SALARY + 1800
      WHEN SALARY < 70000
        SALARY := SALARY + 1200
      WHEN SALARY < 90000
        SALARY := SALARY + 600
      WHEN NONE
        SALARY := SALARY + 300
    END-DECIDE
    END

### On this page

- Prerequisites
- Fundamentals of Debugging
- Session 1 - Analyzing a Natural Error
- Session 2 - Using a Breakpoint
- Session 3 - Using a Watchpoint
- Session 4 - Tracing the Logical Flow of Programs
- Session 5 - Using Statistics about the Program Execution
- Additional Hints for Using the Debugger
- Example Sources