Calculation of permutation and combination using using functions in C

This program is an example of using functions. It teaches you how to declare function, define it and call. Here functions for calculating factorial and permutation/combination is used. Once you see the code you will be able to understand following

• Function declaration, definition, calls.
• Use of switch statement in program.
• How to write structured program.
• How to make menu in C

The complete source code and output is given here…

Source Code

//calculation of permutation and combination using function in C
#include<stdio.h>
#include<conio.h>   //for getch() function
//function declaration must be
//written before main function,
//function definition is optional
//you can write befor or after main
int factorial(int n){
    int fact = 1;
    int i;
    for(i = n; i > 0; i--){
        fact = fact*i;
    }
    return fact;
}
int permutation(int n,int r){
    int per;
    per = factorial(n)/(factorial(n-r));
    return per;
}
int combination(int n,int r){
    int comb; //local variable
    comb = factorial(n)/(factorial(n-r)*factorial(r));
    return comb; //return statement
}
int main(){
    int choice;
    int n,r;
    while(1){
        printf("\n1. Permutation\n2. Combination\n3. Factorial\n");
        printf("Choose option: ");
        scanf("%d",&choice);
        switch(choice){ //start of switch statement
            case 1:
                printf("Enter value of n,r: ");
                scanf("%d%d",&n,&r);
                //calculation of combination with function call
                printf("Permutation P(%d,%d) = %d",n,r,permutation(n,r));
                break;
            case 2:
                printf("Enter value of n,r: ");
                scanf("%d%d",&n,&r);
                printf("Combination C(%d,%d) = %d",n,r,combination(n,r));
                break;
            case 3:
                printf("Enter value of n: ");
                scanf("%d",&n);
                printf("The factorial %d! = %d",n,factorial(n));
                break;
            default: //if user enter other than 1 or 2
                printf("Invalid choice! Enter either 1 or 2");
        } //end of switch statement
        printf("\nWant another calculation?(y/n):");
        if(getche()=='n')
        break;
    }
    return 0;
}//end of main

Output