C #define

The #define directive is used to create macros. Macros are symbolic names that represent a sequence of characters or values. These symbolic names can be used to replace text in your code. Macros are processed by the C preprocessor before the code is compiled, and they are often used to create constants or to define short, reusable code snippets.

Here’s the basic syntax of the #define directive:

 #define macro_name replacement_text

• macro_name is the name you want to give to the macro.
• replacement_text is the text or value that the macro represents.

There are two common use cases for #define:

1. Creating Constants:
   You can use #define to create constants, which are values that don’t change during the program’s execution. For example:

 #define PI 3.14159265359

After defining this macro, you can use PI in your code, and the preprocessor will replace PI with the specified value.

2. Creating Code Macros:
   Macros can be used to create short, reusable code snippets. For example:

 #define SQUARE(x) ((x) * (x))

This macro defines a function-like macro SQUARE that calculates the square of a number. You can use it in your code like this:

 int result = SQUARE(5); // result will be 25

The preprocessor replaces SQUARE(5) with ((5) * (5)).

Here’s an example that demonstrates both constant and code macros:

#include <stdio.h>

#define PI 3.14159265359
#define SQUARE(x) ((x) * (x))

int main() {
    double radius = 5.0;
    double area = PI * SQUARE(radius);
    printf("Area of a circle with radius %.2f is %.2f\n", radius, area);

    return 0;
}

In this example:

• The PI constant is used to represent the mathematical constant π.
• The SQUARE macro is used to calculate the square of the radius.

The C preprocessor replaces PI and SQUARE(radius) with their respective values before the code is compiled, resulting in the calculation of the circle’s area.

Using #define allows you to make your code more readable, maintainable, and flexible by defining meaningful names for constants and creating reusable code snippets.