In this section, we will cover the fundamental syntax and structure of Control Language (CL). Understanding these basics is crucial for writing effective CL programs. We will break down the key components and provide examples to illustrate each concept.

1. CL Program Structure
2. Commands
3. Parameters
4. Comments
5. Labels

A CL program typically consists of a series of commands that are executed sequentially. The basic structure of a CL program is as follows:

• PGM marks the beginning of the program.
• ENDPGM marks the end of the program.

In this example:

• DCL declares a variable.
• CHGVAR changes the value of the variable.
• SNDPGMMSG sends a program message.

Commands are the building blocks of CL programs. Each command performs a specific operation. Commands are written in uppercase and follow a specific syntax.

In this example:

• DCL is the command to declare a variable.
• VAR(&COUNTER) specifies the variable name.
• TYPE(*INT) specifies the variable type.
• LEN(4) specifies the length of the variable.

Parameters are used to provide additional information to commands. They are enclosed in parentheses and separated by spaces.

In this example:

• MSG('Processing Complete') specifies the message to be sent.
• TOPGMQ(*EXT) specifies the target program queue.
• MSGTYPE(*INFO) specifies the message type.

Comments are used to add explanations or notes within the code. They are ignored by the CL interpreter. Comments start with //.

Labels are used to mark specific points in the program. They are useful for controlling the flow of the program, such as in loops or conditional statements. Labels are defined by a name followed by a colon (:).

In this example:

• LOOP: is a label.
• GOTO CMDLBL(LOOP) directs the program flow to the LOOP label.

Write a CL program that:

1. Declares a variable to hold a message.
2. Sets the message to "Welcome to CL Programming!".
3. Sends the message.

Write a CL program that:

1. Declares a counter variable.
2. Initializes the counter to 1.
3. Uses a loop to send a message "Counter is X" where X is the counter value.
4. Increments the counter by 1.
5. Repeats the loop until the counter reaches 5.

In this section, we covered the basic syntax and structure of CL programs, including the use of commands, parameters, comments, and labels. Understanding these fundamentals is essential for writing and reading CL programs. In the next module, we will dive deeper into basic CL commands and their usage.