Functions in C

A function in C is a block of code that performs a specific task. Functions help in code reusability, modular programming, and easy debugging.

Types of Functions

In C, functions are categorized into two types:

• Library Functions: Predefined functions like printf(), scanf(), sqrt(), etc.
• User-Defined Functions: Functions created by the programmer to perform specific tasks.

Function Declaration, Definition, and Calling

Function Declaration

A function must be declared before use. It specifies the function name, return type, and parameters.

int add(int, int);  // Function declaration

Function Definition

A function definition contains the actual implementation.

#include <stdio.h>

// Function definition
int add(int a, int b) {
    return a + b;
}

int main() {
    int sum = add(5, 3);  // Function call
    printf("Sum: %d", sum);
    return 0;
}

Function Calling

To execute a function, it must be called in main() or another function.

Types of Function Arguments

1. Function Without Parameters and Without Return Value

A function that takes no arguments and returns nothing.

#include <stdio.h>

void greet() {
    printf("Hello, Welcome to C Programming!");
}

int main() {
    greet();  // Function call
    return 0;
}

2. Function With Parameters and Without Return Value

A function that takes arguments but does not return any value.

#include <stdio.h>

void display(int num) {
    printf("Number: %d", num);
}

int main() {
    display(10);  // Function call
    return 0;
}

3. Function Without Parameters and With Return Value

A function that does not take arguments but returns a value.

#include <stdio.h>

int getNumber() {
    return 25;
}

int main() {
    int num = getNumber();
    printf("Returned Value: %d", num);
    return 0;
}

4. Function With Parameters and With Return Value

A function that takes arguments and returns a value.

#include <stdio.h>

int multiply(int a, int b) {
    return a * b;
}

int main() {
    int result = multiply(4, 5);
    printf("Multiplication: %d", result);
    return 0;
}

Call by Value vs Call by Reference

Call by Value

In Call by Value, a copy of the argument is passed to the function. Changes in the function do not affect the original variable.

#include <stdio.h>

void modify(int x) {
    x = 20; // Changing value inside the function
}

int main() {
    int num = 10;
    modify(num);
    printf("Value after function call: %d", num); // Output: 10
    return 0;
}

Call by Reference

In Call by Reference, a pointer to the argument is passed, allowing modifications to affect the original variable.

#include <stdio.h>

void modify(int *x) {
    *x = 20; // Modifying the actual value
}

int main() {
    int num = 10;
    modify(&num);
    printf("Value after function call: %d", num); // Output: 20
    return 0;
}

Recursion in C

Recursion is when a function calls itself to solve a problem.

Example: Factorial Using Recursion

#include <stdio.h>

int factorial(int n) {
    if (n == 0) return 1;
    return n * factorial(n - 1);
}

int main() {
    int num = 5;
    printf("Factorial of %d is %d", num, factorial(num));
    return 0;
}

Functions are essential in C programming for structuring code efficiently. They improve code reusability, readability, and modularity.

If you have any questions, feel free to ask. Thank you for reading!