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

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

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.

```
#include <stdio.h>
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.