[pradeep]

In mathematics, the integers a and b are said to be coprime or relatively prime if they have no common factor other than 1 and −1, or equivalently, if their greatest common divisor is 1.

In the program below, I've used the gcf() function to check whether the GCF of the two numbers is 1.

#include <stdio.h>
#include <conio.h>
int gcf( int n , int m ) ;
int lcm( int n , int m ) ;
 
int main()
{
    int a , b ;
    clrscr();

    printf( "Enter two integers\n" ) ;
    scanf( "%d" , &a ) ;
    scanf( "%d" , &b ) ;

    if(gcf(a,b)==1)
    {
        printf("The numbers are co primes");
    }
    else
    {
        printf("The numbers are not co primes");
    }
    getch();
    return 0 ;
}
 
/*
gcf

Calculates the gcf (greatest common factor) for a pair
of integers.  If either number is zero, zero is returned.
Negative inputs are treated as if they were positive.
*/
int gcf( int n , int m )
{
    if( n == 0 || m == 0 )
        return 0 ;

    if( n < 0 ) 
        n = - n ;
    if( m < 0 ) 
        m = - m ;

    /* subtract the larger from the smaller until they are equal */
    while( 1 ) 
        if( n > m )
            n -= m ;
        else if ( n < m )
            m -= n ;
        else
            break ;

    return n ;
}