The #define directive in C is used for creating macros, constants, and inline functions. Let's go through examples of each:

1. Constants using #define:

   • Defining a constant using #define.

    #include <stdio.h>

    // Define a constant
    #define PI 3.14159

    int main() {
        float radius = 5.0;
        float area = PI * radius * radius;

        printf("Area of the circle: %f\n", area);

        return 0;
    }

In this example, PI is a constant with a value of 3.14159. When the code is compiled, the preprocessor replaces all instances of PI with 3.14159.

1. Inline Functions using #define:

   • Creating a simple inline function using #define.

    #include <stdio.h>

    // Define an inline function
    #define SQUARE(x) ((x) * (x))

    int main() {
        int num = 5;
        int result = SQUARE(num);

        printf("Square of %d: %d\n", num, result);

        return 0;
    }

Here, the SQUARE macro is defined to calculate the square of a given value. It's important to note the use of parentheses to ensure proper evaluation, especially when used with expressions.

1. Generic Macros using #define:

   • Creating a generic macro that works with different data types.

    #include <stdio.h>

    // Define a generic max macro
    #define MAX(a, b) ((a) > (b) ? (a) : (b))

    int main() {
        int num1 = 10, num2 = 7;
        int max_result = MAX(num1, num2);

        printf("Max between %d and %d: %d\n", num1, num2, max_result);

        double num3 = 8.5, num4 = 12.3;
        double max_double = MAX(num3, num4);

        printf("Max between %.2f and %.2f: %.2f\n", num3, num4, max_double);

        return 0;
    }

The MAX macro is generic and can be used with different data types. It uses the ternary operator to determine the maximum value.

These examples showcase how #define can be used for creating constants, inline functions, and macros in C. While macros provide a powerful tool for code abstraction and customization, it's essential to use them carefully to avoid unintended side effects and ensure proper code readability.