Difference between Macros and Constants in C

In C programming, macros and constants are both used to represent fixed values, but they differ in how they work and how the compiler treats them.

Macros in C

In C programming, you can use macros to define constants or functions that you want to reuse in your program. Macros are part of the preprocessor directives. The preprocessor reads them and replaces the code before the compiler runs. To create a macro, use the #define directive.

Syntax for Macros:

#define MACRO_NAME value

Example of Macros:

#include <stdio.h>
 
#define PI 3.14159
#define SQUARE(x) ((x) * (x))
 
int main()
{
    // PI is replaced with 3.14159
    printf("Area of circle: %.2f\n", PI * SQUARE(5));
    return 0;
}

• PI is a simple constant.
• SQUARE(x) is a function-like macro that calculates the square of a number.

Constants in C

Constants in C are values that do not change during the execution of a program. Once defined, their values remain fixed. Constants help make your code more readable, maintainable, and bug-free.

Syntax for Constants:

const data_type CONSTANT_NAME = value;

Example of Constants:

#include <stdio.h>
 
int main()
{
    const float PI = 3.14159;
    const int MAX_VALUE = 100;
 
    printf("Area of circle: %.2f\n", PI * 5 * 5);  // Using constant PI
    return 0;
}

PI is a constant that is treated like a variable but its value cannot be changed.

Difference Between Macros and Constants

Here are the main differences between Macros and Constants in C. This table shows how they are defined, how they work, and when to use them.

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