Different ways in C# to find the factorial of a number

Different ways in C# to find the factorial of a number:

In this post, we will learn how to find the factorial of a number in C#. We will write one C# program that will take one number as input from the user and print out the factorial for that number.

Factorial of a number is the multiplication of all numbers from 1 to that number. For example, factorial of 5 is 12345. Finding out a factorial can be done in different ways in C#. We will check these methods to solve it.

Method 1: Using for loop:

Using a for loop, we can find the factorial of a number easily. For example, let’s take a look at the program below:

using System;

public class Program
{
	public static void Main()
	{
		int givenNumber, factorial = 1;

		Console.WriteLine("Enter a number to find the factorial ");
		givenNumber = Convert.ToInt32(Console.ReadLine());

		for(int i = 2; i<= givenNumber; i++){
			factorial *= i;
		}

		Console.WriteLine("Factorial : {0}",factorial);

	}
}

Here,

we have created two variables givenNumber and factorial. givenNumber is used to hold the user given number and factorial to hold the final factorial value.
We are reading the user input number and storing it in the variable givenNumber.
Using a for loop, we are iterating from i = 2 to i = givenNumber. i.e. we are iterating all numbers from 2 to that number.
For each value of i, we are multiplying it with factorial. The initial value of factorial is 1.
Finally, we are printing the value of factorial.

Sample Output:

It will print outputs as like below:

Enter a number to find the factorial
4
Factorial : 24

Enter a number to find the factorial
10
Factorial : 3628800

Method 2: Using a different function:

We can put the factorial part in a different function and call that function directly. For example:

using System;

public class Program
{
	static int getFactorial(int number){
		int factorial = 1;
		for(int i = number; i > 1; i--){
			factorial = factorial * i;
		}
		return factorial;
	}

	public static void Main()
	{
		int givenNumber;

		Console.WriteLine("Enter a number to find the factorial ");
		givenNumber = Convert.ToInt32(Console.ReadLine());

		Console.WriteLine("Factorial : {0}",getFactorial(givenNumber));

	}
}

This time, I kept everything same, only the factorial part is moved to a different function. This function, getFactorial, takes one number as argument and returns the factoral value. We are using a for loop to find the factorial value in this method.

Method 3: Using while loop:

We can use one while loop to do the same thing. The while loop will run from number to 2 in reverse order and multiply all values to find the factorial. Let’s write the program:

using System;

public class Program
{
	static int getFactorial(int number){
		int factorial = 1;
		
		while(number > 1){
			factorial = factorial * number;
			number--;
		}
		return factorial;
	}

	public static void Main()
	{
		int givenNumber;

		Console.WriteLine("Enter a number to find the factorial ");
		givenNumber = Convert.ToInt32(Console.ReadLine());

		Console.WriteLine("Factorial : {0}",getFactorial(givenNumber));

	}
}

This program will give output as like the previous one:

Enter a number to find the factorial 
5
Factorial : 120

Method 4: Recursive approach:

We can also solve it by calling a method recursively. Recursive method calls itself again and again until an end point is reached. The below program shows how to find the factorial recursively in C#.

using System;

public class Program
{
	static int getFactorial(int number){
		if(number == 1){
			return 1;
		}
		return number * getFactorial(number - 1);
	}

	public static void Main()
	{
		int givenNumber;

		Console.WriteLine("Enter a number to find the factorial ");
		givenNumber = Convert.ToInt32(Console.ReadLine());

		Console.WriteLine("Factorial : {0}",getFactorial(givenNumber));

	}
}

Here, we are calling getFactorial method recursively. If the value of number is 2, it returns 2, else it returns number multiplied by calling the same method with number - 1 as the parameter. So, it calls the same method recursively and returns the factorial of number.

If you run this program, it will give a similar output.

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