Permutation and Combination – C PROGRAM

In one of my posts on C Programming, I showed, how to calculate the Factorial of a number.

In this post we will use that program, and extend it to calculate the Combination ^nC_r and the Permutation ^nP_r .

If you haven’t read the post on factorial calculation, then you can check it out here.

Now, a combination is defined as:
^nC_r = \frac{n!}{r!(n-r)!}

and the Permutation is defined as:
^nP_r = \frac{n!}{(n-r)!}

So we will have the user enter their choice, and then prompt the user to enter the r and n
and then return the answer based on their choice.

The program is pretty simple and can be written as shown below.



/*Function that calculates the factorial of a given integer n */
double factorial(int n){
  int i;
  double fact=1;
  return fact;

int main(){
  int n,r,choice;
  printf("\n\nType 1 for Permutation and \n2 for Combination\n");
    printf("Enter n and r for nPr\n");
    scanf("%d %d",&n,&r);
      printf("Sorry! r should be smaller than n\n");
      return 0;
    printf("The permutation (%dP%d)= %f\n",n,r,factorial(n)/factorial(n-r));
  }else if(choice==2){
    printf("Enter n and r for nCr\n");
    scanf("%d %d",&n,&r);
      printf("r should be smaller than n\n");
      return 0;
    printf("The combination (%dC%d)= %f\n",n,r,factorial(n)/(factorial(n-r)*factorial(r)));
    printf("\nPlease enter a valid choice!\n");

As one can see, the program is pretty much self-explanatory.


Some sample outputs have been attached below:

[wpedon id="7041" align="center"]

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