Combination by using factorial function method

Question

I cannot combinate 20 and 17, the program says that the result is 1. Why?? I'm sure my code is right but i just cannot combinate big numbers.

using System;
namespace question
{
    class beat_That
    {
        static int Factorial(int m)
        {
            int result = 1;
            for (int i = 1; i <= m; i++)
            {
                result *= i;
            }
            return result;
        }
        static void Main(string[] args)
        {
            Console.WriteLine("enter number of objects in the set: ");
            int n = Convert.ToInt32(Console.ReadLine());

            Console.WriteLine("enter number to be chosen: ");
            int k = Convert.ToInt32(Console.ReadLine());

            int combination = Factorial(n) / (Factorial(n - k) * Factorial(k));
            Console.WriteLine("C(" + n + ", " + k + ") = " + combination);

            Console.ReadKey();

        }
    }
}

Answer 1

I'm guessing this is a homework assignment? Here are some tips that will hopefully get you going in the right direction:

(1) Typically, .NET classes are Pascal Case , so for example: comb should be Comb . Also, it's better to assign descriptive class names instead of short abbreviations. For clarity I'm going to assume you at least rename comb to Comb so it isn't confused with a variable name, but another option might be Calculator for example.

(2) Check your syntax and any compiler errors. For example, the compiler should be complaining about this line of code: Console.WriteLine("the combination of {0} and {1} is {2}. "),a1,b1,;

(3) Your methods Factorial and Combination are static methods (as opposed to instance methods). This changes how you call these methods. Static methods are called without an instance, for example: Comb.Combination(..)

(4) Make sure you test various inputs! Your implementation of Combination is not quite correct, but I'll leave that as an exercise to figure out why.