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Factorial Number Program in C# with Examples

In this article, I am going to discuss the Factorial Number Program in C# with Examples. Please read our previous article where we discussed the Armstrong Number Program in C# with examples. In many interviews, the interviewer asked this question in many different ways. As part of this article, we are going to discuss the following pointers.

1. What is factorial of a number?
2. Factorial of a number using for loop, while loop and do-while loop in C#.
3. Factorial of a number using the recursive function in C#.

What is Factorial of a number?

The Factorial of a number (let say n) is nothing but the product of all positive descending integers of that number. Factorial of n is denoted by n!. Please have a look at the following image which shows how to calculate the factorials of a number.

Factorial Number Program in C# using for loop:

In the following example, we take the number from the console and then calculate the factorial of that number using for loop.

using System;
namespace LogicalPrograms
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.Write("Enter a Number : ");
            int number = int.Parse(Console.ReadLine());

            int factorial = 1;
            for (int i = 1; i <= number; i++)
            {
                factorial = factorial * i;
            }
            Console.Write($"Factorial of {number}  is: {factorial}");
            
            Console.ReadLine();
        }
    }
}

Output:

Factorials of a number using while loop in C#:

In the following example, we use while loop to calculate the factorial of a number.

using System;
namespace LogicalPrograms
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.Write("Enter a Number : ");
            int number = int.Parse(Console.ReadLine());

            long factorial = 1;
            while (number != 1)
            {
                factorial = factorial * number;
                number = number - 1;
            }
            
            Console.Write($"Factorial is: {factorial}");           
            Console.ReadLine();
        }
    }
}

Output:

Factorial of a number using Recursive Function in C#:

In the following program, we use a recursive function to calculate the factorial of a given number.

using System;
namespace LogicalPrograms
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.Write("Enter a Number : ");
            int number = int.Parse(Console.ReadLine());

            long factorial = RecursiveFactorial(number);
            Console.Write($"Factorial of {number} is: {factorial}");    
            
            Console.ReadLine();
        }

        static long RecursiveFactorial(int number)
        {
            if (number == 1)
            {
                return 1;
            } 
            else
            {
                return number * RecursiveFactorial(number - 1);
            }    
        }
    }
}

Output:

Factorial of a number using the do-while loop in C#:

In the below program, we use the do-while loop to calculate the factorial of a given number. The number here we are taking from the console.

using System;
namespace LogicalPrograms
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.Write("Enter a Number : ");
            int number = int.Parse(Console.ReadLine());
            long factorial =  1;

            do
            {
                factorial = factorial * number;
                number--;
            } while (number > 0);

            Console.Write($"The Factorial is: {factorial}");
            Console.ReadLine();
        }      
    }
}

Output:

In the next article, I am going to discuss the Sum Of Digits Program in C# with some examples. Here, in this article, I try to explain the different ways to implement the Factorial Number Program in C# with examples.

Introduction to Factorial in C#

In this section, we shall see the factorial in c# in detail. Factorial is a very important concept in the area of mathematics like in algebra or in mathematics analytics. It is denoted by sign of exclamation (!). Factorial is any positive integer k, which is denoted by k! It is the product of all positive integers which are less than or equal to k.

k!= k * (k-1) *(k-2) *(k-3) *(k-4) *…….3 *2 * 1.

Logic to Calculate Factorial of A Given Number

For example, if we want to calculate the factorial of 4 then it would be,

Example #1

4! = 4 * (4-1) *(4-2) * (4-3)

4! = 4 * 3 * 2 * 1

4! = 24.

So factorial of 4 is 24

Example #2

6! = 6 * (6-1)* (6-2)* (6-3) * 6-4)* (6-5)

6! = 6*5*4*3*2*1

6! = 720

So factorial of 6 is 720

Similarly, by using this technique we can calculate the factorial of any positive integer. The important point here is that the factorial of 0 is 1.

0! =1.

There are many explanations for this like for n! where n=0 signifies product of no numbers and it is equal to the multiplicative entity. {displaystyle {binom {0}{0}}={frac {0!}{0!0!}}=1.}

The factorial function is mostly used to calculate the permutations and combinations and also used in binomial. With the help of the factorial function, we can also calculate the probability. For example in how many ways we can arrange k items. We have k choices for the first thing, So for each of these k choices, we left with k-1 choices for the second things (because first choice has already been made), so that now we have k(k-1) choices, so now for the third choice we have k(k-1)(k-2) choices and so on until we get one on thing is remaining. So altogether we will have k(k-1)(k-2)(k-3)…3..1.

Another real-time example is supposed we are going to a wedding and we want to choose which blazer to take. So let’s suppose we have k blazers and but have room to pack the only n. So how many ways we can use n blazers from a collection of k blazers k!/(n!.(k-n)!).

Examples of Factorial in C#

Below are the examples to show how we can calculate factorial of any number in different ways,

Example #1

1. In these examples, for loop is used to calculate the factorial of a number.

Code:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace Factorial
{
class Program
{
static void Main()
{
int a = 7;
int fact = 1;
for (int x = 1; x <= a; x++)
{
fact *= x;
}
Console.WriteLine(fact);
Console.ReadLine();
}
}
}

In this example, the variable of integer data type is initialized and for loop is used to calculate the number.

Output:

2. In this example, the user is allowed to enter the number to calculate the factorial.

Code:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using  System.Threading.Tasks;
namespace FactorialExample
{
class Program
{
static void Main()
{
Console.WriteLine("Enter the number: ");
int a = int.Parse(Console.ReadLine());
int fact = 1;
for (int x = 1; x <= a; x++)
{
fact *= x;
}
Console.WriteLine(fact);
Console.ReadLine();
}
}
}

Output:

Example #2

1. In these examples, for loop is used to calculate the factorial of a number.

Code:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace Factorial
{
class Program
{
static void Main()
{
int a = 10;
int fact = 1;
while (true)
{
Console.Write(a);
if (a == 1)
{
break;
}
Console.Write("*");
fact *= a;
a--;
}
Console.WriteLine(" = {0}", fact);
Console.ReadLine();
}
}
}

Output:

2. In these examples, while loop is used to calculate the factorial of a number.

Code:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace FactorialExample
{
class Program
{
static void Main()
{
Console.WriteLine("Enter the number: ");
int a = int.Parse(Console.ReadLine());
int fact = 1;
while(true)
{
Console.Write(a);
if(a==1)
{
break;
}
Console.Write("*");
fact *= a;
a--;
}
Console.WriteLine(" = {0}", fact);
Console.ReadLine();
}
}
}

Output:

Example #3

1. In this example, do-while is used to calculate the factorial of a number.

Code:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace Factorial
{
class Program
{
static void Main()
{
int a = 6;
int fact = 1;
do
{
fact *= a;
a--;
} while (a > 0);
Console.WriteLine("Factorial = {0}", fact);
Console.ReadLine();
}
}
}

Output:

2. In this example, do-while is used to calculate the factorial of a number.

Code:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace FactorialExample
{
class Program
{
static void Main()
{
Console.Write("Enter the number: ");
int a = int.Parse(Console.ReadLine());
int fact = 1;
do
{
fact *= a;
a--;
} while (a > 0);
Console.WriteLine("Factorial = {0}", fact);
Console.ReadLine();
}
}
}

Output:

Example #4

1. In this example, a recursive function is used to calculate the factorial of a number.

Code:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace Factorial
{
class Program
{
static void Main()
{
int n= 5;
long fact = Fact(n);
Console.WriteLine("factorial is {1}", n, fact);
Console.ReadKey();
}
private static long Fact(int n)
{
if (n == 0)
{
return 1;
}
return n * Fact(n - 1);
}
}
}

In the above example, the factorial of a number is achieved by using recursion. The idea behind the recursion is to solve the problem in small instances. So whenever a function creating a loop and calling itself, it’s called recursion.

Output:

2. In this example, a recursive function is used to calculate the factorial of a number.

Code:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace FactorialExample
{
class Program
{
static void Main()
{
Console.WriteLine("Enter the number");
int n = Convert.ToInt32(Console.ReadLine());
long fact = Fact(n);
Console.WriteLine("factorial is {1}", n, fact);
Console.ReadKey();
}
private static long Fact(int n)
{
if (n == 0)
{
return 1;
}
return n * Fact(n - 1);
}
}
}

Output:

Conclusion

So the concept of factorial is very important in areas of mathematics such as binomials and permutations and combinations, and this is how we can print the factorial of any number by using multiple methods such as for, while, do-while, function, etc.

Recommended Articles

This is a guide to Factorial in C#. Here we discuss the basic concept of factorial in c# along with different examples and code implementation. You may also look at the following articles to learn more –

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