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Introduction

COBOL (Common Business-Oriented Language) is a high-level programming language designed for business applications. OpenVMS supports COBOL, allowing developers to create robust and efficient business applications. This section will cover the basics of using COBOL on OpenVMS, including setting up the environment, writing and compiling COBOL programs, and practical examples.

Setting Up the Environment

Before you start writing COBOL programs on OpenVMS, you need to ensure that the COBOL compiler is installed and properly configured.

Steps to Set Up COBOL on OpenVMS

Check for COBOL Compiler Installation:
```
$ SHOW LOGICAL COBOL$COMPILER
```
If the compiler is installed, this command will display the logical name of the COBOL compiler.
Install COBOL Compiler (if not installed): Follow the OpenVMS documentation to install the COBOL compiler package.
Set Up Environment Variables: Ensure that the necessary environment variables are set. This can typically be done in your login script.
```
$ DEFINE COBOL$COMPILER SYS$SYSTEM:COBOL.EXE
```

Writing a COBOL Program

A COBOL program consists of four main divisions: Identification Division, Environment Division, Data Division, and Procedure Division. Below is a simple COBOL program that prints "Hello, OpenVMS!".

Example: Hello, OpenVMS!

IDENTIFICATION DIVISION.
PROGRAM-ID. HELLO-OPENVMS.

ENVIRONMENT DIVISION.

DATA DIVISION.

PROCEDURE DIVISION.
    DISPLAY "Hello, OpenVMS!".
    STOP RUN.

Explanation

IDENTIFICATION DIVISION: This section identifies the program.
PROGRAM-ID: Specifies the name of the program.
ENVIRONMENT DIVISION: Used to specify the environment in which the program will run (not used in this simple example).
DATA DIVISION: Used to define variables and data structures (not used in this simple example).
PROCEDURE DIVISION: Contains the executable code. The DISPLAY statement outputs text to the screen, and STOP RUN terminates the program.

Compiling and Running COBOL Programs

Compiling the Program

To compile the COBOL program, use the following command:

$ COBOL HELLO-OPENVMS.COB

This command will generate an object file (HELLO-OPENVMS.OBJ).

Linking the Program

Next, link the object file to create an executable:

$ LINK HELLO-OPENVMS

This command will produce an executable file (HELLO-OPENVMS.EXE).

Running the Program

Finally, run the executable:

$ RUN HELLO-OPENVMS

You should see the output:

Hello, OpenVMS!

Practical Exercises

Exercise 1: Simple Arithmetic Operations

Write a COBOL program that performs basic arithmetic operations (addition, subtraction, multiplication, and division) on two numbers provided by the user.

Solution

IDENTIFICATION DIVISION.
PROGRAM-ID. ARITHMETIC-OPERATIONS.

ENVIRONMENT DIVISION.

DATA DIVISION.
WORKING-STORAGE SECTION.
01 NUM1 PIC 9(5).
01 NUM2 PIC 9(5).
01 RESULT PIC 9(10).

PROCEDURE DIVISION.
    DISPLAY "Enter first number: ".
    ACCEPT NUM1.
    DISPLAY "Enter second number: ".
    ACCEPT NUM2.

    COMPUTE RESULT = NUM1 + NUM2.
    DISPLAY "Addition: " RESULT.

    COMPUTE RESULT = NUM1 - NUM2.
    DISPLAY "Subtraction: " RESULT.

    COMPUTE RESULT = NUM1 * NUM2.
    DISPLAY "Multiplication: " RESULT.

    IF NUM2 NOT = 0 THEN
        COMPUTE RESULT = NUM1 / NUM2
        DISPLAY "Division: " RESULT
    ELSE
        DISPLAY "Division by zero is not allowed.".

    STOP RUN.

Exercise 2: String Manipulation

Write a COBOL program that accepts a string from the user and displays it in reverse order.

Solution

IDENTIFICATION DIVISION.
PROGRAM-ID. REVERSE-STRING.

ENVIRONMENT DIVISION.

DATA DIVISION.
WORKING-STORAGE SECTION.
01 INPUT-STRING PIC X(50).
01 REVERSED-STRING PIC X(50).
01 I PIC 99.
01 LENGTH PIC 99.

PROCEDURE DIVISION.
    DISPLAY "Enter a string: ".
    ACCEPT INPUT-STRING.

    COMPUTE LENGTH = FUNCTION LENGTH(INPUT-STRING).

    PERFORM VARYING I FROM 1 BY 1 UNTIL I > LENGTH
        MOVE INPUT-STRING(LENGTH - I + 1:1) TO REVERSED-STRING(I:1)
    END-PERFORM.

    DISPLAY "Reversed string: " REVERSED-STRING.

    STOP RUN.

Common Mistakes and Tips

Syntax Errors: COBOL is very particular about syntax and formatting. Ensure that each division, section, and statement is correctly placed.
Data Types: Be mindful of the data types and their sizes. COBOL uses specific picture clauses (PIC) to define data types.
Environment Setup: Ensure that the COBOL compiler and environment variables are correctly set up before compiling and running programs.

Conclusion

In this section, you learned how to set up the COBOL environment on OpenVMS, write simple COBOL programs, and compile and run them. You also practiced with exercises to reinforce your understanding. In the next module, we will explore interfacing with system services using COBOL on OpenVMS.

Using COBOL on OpenVMS

Introduction

Setting Up the Environment

Steps to Set Up COBOL on OpenVMS

Writing a COBOL Program

Example: Hello, OpenVMS!

Explanation

Compiling and Running COBOL Programs

Compiling the Program

Linking the Program

Running the Program

Practical Exercises

Exercise 1: Simple Arithmetic Operations

Solution

Exercise 2: String Manipulation

Solution

Common Mistakes and Tips

Conclusion

OpenVMS Programming Course

Module 1: Introduction to OpenVMS

Module 2: Basic OpenVMS Commands

Module 3: OpenVMS File System

Module 4: Scripting with DCL

Module 5: OpenVMS System Management

Module 6: Networking on OpenVMS

Module 7: Advanced OpenVMS Programming

Module 8: OpenVMS Clustering

Module 9: OpenVMS Security

Module 10: Troubleshooting and Optimization