C program for combination

C program for combination. Combination is way of selecting a set of things out of a group. C program made to find permutation is similar. The main difference between permutation and combination is that,  in combination order does not matter while in permutation order matters. With combination we can find in how many ways can n objects or a group of an objects can be selected if r objects are selected at a  time. To find Combination we need to know how factorial of of number is calculated in c program. You can see following two programs to implement c program for factorial :

• C program to find factorial of a number
• C program to find factorial of a number using recursion

For example : Suppose we are having 5 objects. Then we can select 2 objects in C(5,2) = 10 i.e in 504 ways. combination can be calculated by the formula : C(n,r) = n!/((n-r)!r!) where n = number of available objects
and     r = number of selected objects from the group.

C program for combination :

#include<stdio.h>
#include<conio.h>

int fact(int);

int main()
{
    int p,r,n;

    printf(" Enter number for the calculating combination C(n,r)\n");
    printf("Enter n value : ");
    scanf("%d",&n);
    printf("\nEnter r value : ");
    scanf("%d",&r);
    p=fact(n)/(fact(n-r)*fact(r));
    printf("\nFactorial of C(%d,%d) = %d",n,r,p);
    getch();
}

int fact(int c)
{
    int f=1;
    while(c>0)
    {
        f=f*c;
        c--;
    }
    return f;
}

Output of C program for combination :