C Programming – Day 7 | Functions in C Definition, Types & Examples for Beginners

FUNCTIONS IN C

DAY - 7

✅ We keep learning without stopping 🚀

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📍 Day-7 — Functions in C

Today we will learn:

✅ What is a function?
✅ Types of functions
✅ Function declaration, definition, calling
✅ Passing arguments
✅ Return values
✅ Task + Quiz

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✅ 1️⃣ What is a Function?

📌 A function is a block of code that performs a specific task
📌 Written once — used many times ✅

Example:

#include <stdio.h>

void hello(){
    printf("Hello, World!");
}

int main(){
    hello();
    return 0;
}

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✅ 2️⃣ Function Structure

returnType functionName(parameter) {
    // code
    return value; // if needed
}

Example: Function that returns sum

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

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✅ 3️⃣ Function with Parameters & Return

#include <stdio.h>

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

int main(){
    int result = mul(4, 5);
    printf("Result = %d", result);
    return 0;
}

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✅ 4️⃣ Function Prototype (Declaration)

📌 Write before main() if function defined below

int sum(int, int); // Prototype

int main(){
    printf("%d", sum(3,4));
}

int sum(int a, int b){
    return a+b;
}

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✅ 5️⃣ Types of Functions

Type	Example
No parameter, No return	void hello()
Parameter, No return	void print(int x)
No parameter, Return value	int roll()
Parameter, Return value	int add(int a,int b)

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🧪 Practice Example: Check Even or Odd (Function)

#include <stdio.h>

void checkEvenOdd(int n){
    if(n % 2 == 0)
        printf("Even");
    else
        printf("Odd");
}

int main(){
    int x;
    scanf("%d", &x);
    checkEvenOdd(x);
}

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✅ Task-7

Write a program to:

✔ Create a function named isPrime(int n)
✔ Return:

• 1 → Prime

• 0 → Not Prime
  ✔ In main(), input a number and check prime or not

Example Output:

17 is prime

📌 Hint:

• Prime number has only 2 divisors

• Use loop from 2 to n/2

✅ Submit your code — I will correct if needed

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📝 Quick Quiz — Day-7

Reply like: 1A, 2C, 3B

1️⃣ A function that returns nothing uses:
A) void
B) int
C) float

2️⃣ Which contains the main execution of program?
A) sum()
B) printf()
C) main()

3️⃣ Function prototype is written to:
A) reduce memory
B) tell compiler about function before use
C) stop execution

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🎯 After you finish Day-7:

➡ We start Day-8: Pointers 🔥

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Whenever you’re ready — send:

👉 Task-7 Code
👉 Day-7 Quiz Answers

I’m here with you till complete success! ✅💪

✅ NEXT - DAY - 8