In this section, we will delve into the concepts of functions and subroutines in REXX. These are essential for writing modular, reusable, and maintainable code. We will cover the following topics:
- Introduction to Functions and Subroutines
- Defining and Calling Functions
- Passing Arguments
- Returning Values
- Practical Examples
- Exercises
- Introduction to Functions and Subroutines
Functions and subroutines are blocks of code designed to perform specific tasks. They help in breaking down complex problems into smaller, manageable parts. In REXX, functions and subroutines can be user-defined or built-in.
- Functions: Return a value and can be used in expressions.
- Subroutines: Perform tasks but do not return a value directly.
- Defining and Calling Functions
Defining a Function
A function in REXX is defined using the RETURN statement to return a value. Here is the basic syntax:
Calling a Function
A function is called by using its name followed by parentheses. If the function takes arguments, they are passed within the parentheses.
Example
/* Define a function to add two numbers */ addNumbers: PROCEDURE ARG num1, num2 sum = num1 + num2 RETURN sum /* Call the function */ result = addNumbers(5, 10) SAY "The sum is:" result
- Passing Arguments
Arguments are passed to functions and subroutines using the ARG statement. You can pass multiple arguments separated by commas.
Example
/* Define a function to concatenate two strings */
concatStrings: PROCEDURE
ARG str1, str2
result = str1 || str2
RETURN result
/* Call the function */
result = concatStrings("Hello, ", "World!")
SAY result
- Returning Values
The RETURN statement is used to return a value from a function. The value can be of any data type, such as a number, string, or even another function's result.
Example
/* Define a function to calculate the factorial of a number */ factorial: PROCEDURE ARG num IF num = 0 THEN RETURN 1 result = num * factorial(num - 1) RETURN result /* Call the function */ result = factorial(5) SAY "The factorial of 5 is:" result
- Practical Examples
Example 1: Function to Check Even or Odd
/* Define a function to check if a number is even or odd */ isEven: PROCEDURE ARG num IF num // 2 = 0 THEN RETURN "Even" ELSE RETURN "Odd" /* Call the function */ result = isEven(7) SAY "The number 7 is:" result
Example 2: Subroutine to Print a Message
/* Define a subroutine to print a message */ printMessage: PROCEDURE ARG message SAY message /* Call the subroutine */ CALL printMessage "Hello, REXX!"
- Exercises
Exercise 1: Create a Function to Calculate the Area of a Rectangle
Task: Write a function calculateArea that takes the length and width of a rectangle as arguments and returns the area.
/* Define the function */ calculateArea: PROCEDURE ARG length, width area = length * width RETURN area /* Call the function */ result = calculateArea(5, 10) SAY "The area of the rectangle is:" result
Exercise 2: Create a Subroutine to Print a Multiplication Table
Task: Write a subroutine printMultiplicationTable that takes a number as an argument and prints its multiplication table up to 10.
/* Define the subroutine */
printMultiplicationTable: PROCEDURE
ARG num
DO i = 1 TO 10
SAY num "x" i "=" num * i
END
/* Call the subroutine */
CALL printMultiplicationTable 5Conclusion
In this section, we have covered the basics of functions and subroutines in REXX. We learned how to define and call functions, pass arguments, and return values. We also explored practical examples and exercises to reinforce the concepts. Understanding functions and subroutines is crucial for writing efficient and modular REXX programs. In the next section, we will explore built-in functions in REXX.
REXX Programming Course
Module 1: Introduction to REXX
- What is REXX?
- Setting Up the REXX Environment
- Hello World in REXX
- Basic Syntax and Structure
- Variables and Data Types
Module 2: Basic Programming Concepts
- Operators and Expressions
- Control Structures: IF/THEN/ELSE
- Loops: DO and LEAVE
- Input and Output
- Basic String Manipulation
Module 3: Intermediate REXX Programming
Module 4: Advanced REXX Programming
- Advanced String Manipulation
- Parsing Techniques
- Interfacing with External Programs
- REXX Macros
- Performance Optimization