C Program To Find GCD and LCM of Two Numbers

Lets write a C program to find GCD(Greatest Common Divisor) or HCF(Highest common Factor) and LCM(Least Common Multiple) of 2 user entered integer numbers.

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GCD or HCF: Largest Integer that can divide both the numbers without any remainder or with 0 as remainder.
C Program to Find GCD or HCF of Two Numbers

Least Common Multiple(LCM): is the smallest positive integer that is perfectly divisible by the given integer values.
C Program to Find LCM of Two Numbers
Biggest of Two Numbers Using Ternary Operator: C

Logic To Find GCD and LCM of Two Integer Numbers.

We ask the user to enter 2 integer numbers. Next we find the smallest number among the two. Example, if num1 = 2 and num2 = 3. We can’t have any number bigger than 2, which will divide num1 and have reminder as 0.

Further explanation to find GCD or HCF is present in detail in this article: C Program to Find GCD or HCF of Two Numbers

Formula To Calculate LCM

Once we get the GCD, we use the below formula to calculate LCM.

LCM = ( num1 * num2 ) / GCD;

Source Code: C Program To Find GCD and LCM of Two Numbers

 
#include < stdio.h >

int main()
{
    int num1, num2, gcd, lcm, count = 1, small;

    printf("Enter 2 integer numbers\n");
    scanf("%d%d", &num1, &num2);

    small = (num1 < num2) ? num1 : num2;

    while(count <= small)
    {
        if(num1 % count == 0 && num2 % count == 0)
        {
            gcd = count;
        }
        count++;
    }

    lcm = ( num1 * num2 ) / gcd;

    printf("GCD = %d\nLCM = %d\n", gcd, lcm);

    return 0;
}

Output 1:
Enter 2 integer numbers
30
40
GCD = 10
LCM = 120

Output 2:
Enter 2 integer numbers
12
24
GCD = 12
LCM = 24

C Program To Find GCD and LCM of Two Numbers

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