Introduction to Programming in C

📘 Functions in C (Declaration, Definition, Recursion)

Functions are blocks of code designed to perform a specific task. They help organize code, reduce redundancy, and improve readability and maintenance. C supports both user-defined and library functions.

🔹 Types of Functions

• Library Functions: Predefined, e.g., printf(), scanf(), sqrt()
• User-defined Functions: Created by the programmer

🛠 Function Structure

Every user-defined function in C has three key parts:

• Declaration: The function prototype
• Definition: The actual code block
• Calling: Executing the function

Example:

// Function Declaration
int add(int a, int b);

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

// Function Call
int result = add(5, 10);
printf("Sum = %d", result);

🧠 Function Declaration

Also called a function prototype. It tells the compiler about the function's name, return type, and parameters before its actual definition.

int multiply(int x, int y);

🧱 Function Definition

Contains the logic that executes when the function is called.

int multiply(int x, int y) {
    return x * y;
}

📞 Function Call

You invoke the function with actual arguments.

int result = multiply(3, 4);

📂 Function with No Arguments & No Return

void greet() {
    printf("Welcome to UdaanPath!\n");
}

greet();

🔁 Recursion in C

A function that calls itself is recursive. It's used to solve problems like factorial, Fibonacci, etc.

Factorial using Recursion:

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

Calling factorial(5) returns 120.

⚠️ Recursive vs Iterative Approach

📚 Practice Tasks

1. Create a function to find the largest of three numbers.
2. Write a recursive function to calculate the nth Fibonacci number.
3. Write a function to check if a number is prime.
4. Create a calculator using switch-case with functions for each operation.

✅ Summary

• Functions modularize your code and improve readability.
• They consist of declaration, definition, and call.
• Recursive functions are useful for certain problems but can be memory-intensive.

🚀 Coming Next

In the next chapter, we’ll explore Arrays in C — how to store and access multiple values using a single variable.