Friday, August 12, 2011

Calculation of permutation and combination using functions in C

This program is an example of using functions. It teaches you how to declare a 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 a program.
  • How to write a structured program.
  • How to make menu in C

The complete source code and output are given below.


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
factorial

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