Write a program to find GCD of two numbers.

gcd_calculator.c

#include <stdio.h>

int main() {
    int a, b, i, gcd;

    printf("Enter two numbers: ");
    scanf("%d %d", &a, &b);

    // Find the minimum of a and b
    int min = (a < b) ? a : b;

    for(i = 1; i <= min; i++) {
        if(a % i == 0 && b % i == 0) {
            gcd = i;
        }
    }

    printf("GCD of %d and %d is %d\n", a, b, gcd);

    return 0;
}

✅ Step-by-Step Explanation

🔹 1. Input

• User enters two numbers (say a = 48, b = 18)
• scanf() reads both integers from standard input

🔹 2. Find the smaller number

• GCD can never be greater than the smaller number
• Ternary operator (a < b) ? a : b determines the minimum

🔹 3. Check common divisors

for(i = 1; i <= min; i++) {
    if(a % i == 0 && b % i == 0) {
        gcd = i;
    }
}

• Loop from 1 to the smaller number
• Modulo operator % checks divisibility
• When both numbers are divisible by i, update gcd

🔹 4. Output

• After the loop ends, gcd holds the largest common divisor
• printf() displays the final result

🖨️ Example Run

Input:

Enter two numbers: 48 18

Output:

GCD of 48 and 18 is 6

📌 Key Concepts Covered

Loop (for)

To check all possible divisors from 1 to the smaller number

Modulo operator %

To test divisibility of both numbers by the current index

Decision making (if)

Conditional statement to update GCD when common divisor found

Basic I/O

scanf() for input and printf() for output

Ternary operator

Compact conditional to find minimum of two numbers