C++ Program to Compute Combinations using Factorials

This is a C++ to compute combinations using factorials.

1. This algorithm prints a total number of combination possible for given n and r value.
2. The time complexity of this algorithm is O(n).

1. This algorithm takes the input of n and r value.
2. Print the result using ( n! / (r! * (n-r)!)).
3. Exit.

C++ Program to compute combinations using factorials.
This program is successfully run on Dev-C++ using TDM-GCC 4.9.2 MinGW compiler on a Windows system.

#include<iostream>
 
using namespace std;
 
// A function to find the factorial.
int factorial(int n)
{
	int i;
	for(i = n-1; i > 1; i--)
		n *= i;
 
	return n;
}
 
int main()
{
	int n, r,  result;
	cout<<"A program to find combination from nCr format using ( n! / (r! * (n-r)!))";
	cout<<"\n\n\tEnter the value of n: ";
	cin>>n;
	cout<<"\tEnter the value of r: ";
	cin>>r;
 
	// Get result using formula to calculate combinations.
	result = factorial(n)/(factorial(r)*factorial(n-r));
 
	cout<<"\nThe number of possible combinations is: "<<result;
}

1. Take the input of n and r.
2. Using factorial(), calculate values for n!, r! and (n-r)!.
3. Using ( n! / (r! * (n-r)!)), print the result.
4. Exit.

Case 1:
A program to find combination from nCr format using ( n! / (r! * (n-r)!))
 
        Enter the value of n: 5
        Enter the value of r: 3
 
The number of possible combinations is: 10
 
Case 2:
A program to find combination from nCr format using ( n! / (r! * (n-r)!))
 
        Enter the value of n: 13
        Enter the value of r: 4
 
The number of possible combinations is: 221

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