In this section, we will cover the fundamental syntax and structure of REXX programs. Understanding these basics is crucial for writing and reading REXX code effectively.

1. Program Structure
2. Comments
3. Statements and Instructions
4. Whitespace and Line Continuation
5. Case Sensitivity

A REXX program is a sequence of instructions that the interpreter executes. Here is a simple example of a REXX program:

• Comments: Comments in REXX are enclosed within /* and */. They can span multiple lines.
• Instructions: Each instruction is typically written on a new line.

Comments are used to explain the code and are ignored by the interpreter. They can be single-line or multi-line.

REXX instructions are the commands that the interpreter executes. Each instruction should be on a new line. Here are some basic instructions:

• SAY: Outputs text to the screen.
• PULL: Reads input from the user.

Example:

REXX is not sensitive to whitespace, meaning spaces and tabs are generally ignored. However, for readability, it is good practice to use consistent indentation.

If an instruction is too long to fit on one line, you can continue it on the next line using a comma , at the end of the line.

Example:

REXX is case-insensitive for keywords and instructions, but it is case-sensitive for string literals.

Example:

Let's put these concepts together in a simple REXX program:

1. Comments: The program starts with a comment explaining its purpose.
2. SAY Instruction: Prompts the user to enter their favorite programming language.
3. PULL Instruction: Reads the user's input into the variable language.
4. IF/THEN/ELSE Structure: Checks if the input is "REXX" and responds accordingly.

Write a REXX program that asks the user for their age and then prints a message based on the input.

Solution:

Modify the above program to handle invalid input (non-numeric values).

Solution:

• Forgetting to close comments: Ensure every /* has a corresponding */.
• Misusing case sensitivity: Remember that string comparisons are case-sensitive.
• Ignoring whitespace: While REXX ignores extra spaces, consistent indentation improves readability.

In this section, we covered the basic syntax and structure of REXX programs, including comments, statements, whitespace handling, and case sensitivity. These fundamentals are essential for writing clear and effective REXX code. In the next section, we will delve into variables and data types, building on the foundation we've established here.