Question

My question is if n<r when there is no loop. I can't enter numbers again.Where is the problem? How do it?

#include

int fact(int no)
{
if (no == 0)
return 1;
return no * fact(no - 1);
}

int calc(int n, int r,int *com,int *per) //as given in question formula of permutation n!/(n-r)!
{
*com=fact(n)/(fact(r)*fact(n-r));
*per=fact(n)/fact(n-r);
}

int main()
{
int n=0,r=0,co,pe;
while(n<=0 || r<=0)
{
printf("Enter N value:");
scanf("%d",&n);
printf("Enter R value:");
scanf("%d",&r);

if(n {
printf("N value should be greater than R value! try again.");
return(0);
}

else if(n<0 || r<0)
{
printf("N or R values should be equal or greater than Zero. Bye!\n");
return(0);
}

}
calc(n,r,&co,&pe);
printf("Combination : ( %d,%d ) = %.2d \n",n,r,co);
printf("permutation : ( %d,%d ) = %.2d \n",n,r,pe);
}

Answer 1

#include<stdio.h>

int fact(int no)

{

    if (no == 0)

        return 1;

    return no * fact(no - 1);

}

int calc(int n, int r,int *com,int *per) //as given in question formula of permutation n!/(n-r)!

{

    *com=fact(n)/(fact(r)*fact(n-r));

    *per=fact(n)/fact(n-r);

}

int main()

{

    int n=0,r=0,co,pe;

   

    // infinite loop

    while(true)

    {

        printf("Enter N value:");

        scanf("%d",&n);

        printf("Enter R value:");

        scanf("%d",&r);

       

        // if n is smaller than equal to r

        if( n <= r ){

            printf("N value should be greater than R value! try again.");

           

            // as we want to loop again, we will nit use return as it will terminate the program

            // we wil loop again to get user input which is correct

//          return(0);

        }

        else if( n<0 || r<0 )

        {

            printf("N or R values should be equal or greater than Zero. Bye!\n");

            return(0);

        }

        // if both the values are valid, exit the loop

        else if( n > 0 && r > 0 )

            break;

           

        printf("\n\n");

    }

    calc(n,r,&co,&pe);

    printf("Combination : ( %d,%d ) = %.2d \n",n,r,co);

    printf("permutation : ( %d,%d ) = %.2d \n",n,r,pe);

}

Sample Output