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In this example, you will learn to find the GCD (Greatest Common Divisor) of two positive integers entered by the user using recursion.

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To understand this example, you should have the knowledge of the following C programming topics:

• C Functions
• C User-defined functions
• C Recursion

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This program takes two positive integers as input from the user and calculates GCD using recursion.

Visit this page to learn how you can calculate the GCD using loops.

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GCD of Two Numbers using Recursion

#include 
int hcf(int n1, int n2);
int main() {
    int n1, n2;
    printf("Enter two positive integers: ");
    scanf("%d %d", &n1, &n2);
    printf("G.C.D of %d and %d is %d.", n1, n2, hcf(n1, n2));
    return 0;
}

int hcf(int n1, int n2) {
    if (n2 != 0)
        return hcf(n2, n1 % n2);
    else
        return n1;
}

Output

Enter two positive integers: 366
60
G.C.D of 366 and 60 is 6.

In this program, recursive calls are made until the value of n2 is equal to 0.