# How to Find Factorial of a Number Using Recursion

Posted September 5, 2019 by Joudet Ahsan in C programming, Computer programming

Recursion is maybe the easiest yet most problematic concept for the beginners to grasp. But you will get hand of this concept after this Tech-Recipe. Click on “Continue Reading” to read about Recursion and a very easy example.

This tech-recipe will introduce you to the concept of recursion. With the simple example of Factorial of a Number Using Recursion.

### What is Recursion

Recur simply means to reoccur or to happen again. Recursion is a major programming concept in Computer science. Recursion is a process in which function calls itself. The function thus would be called a recursive function.

Sometimes it is easier to define the problem in terms of the problem itself. Especially for the problems that can be broken down into simpler versions

### Example:

Factorial Problems

## 6!=6x5x4x3x2x1! —–> 12

Now this problem can be broken down into simpler versions for itself.

We could write

### 6!=6×5! —–> 12

In general, we can express the factorial function as follows:

### n! = n * (n-1)!

Is this correct? Well… almost.

The factorial function is only defined for positive integers. So we should be a bit more precise:

### n! = 1 (if n is equal to 1)

n! = n * (n-1)! (if n is larger than 1)

For certain problems, a recursive solution often leads to short and elegant code.

Compare the recursive solution with the iterative solution:

Here’s how you can write a Recursive solution of Factorial Problem

Step-by-Step Procedure:

### Factorial of a Number Using Recursion

1. Add required libraries.

2. Make a function that will receive an integer parameter and will return an integer. [So a parameter can be passed to this function. This function will compute the factorial and will return it.]

3. Write the code that will calculate the factorial.

4. A recursive function always has to bottom out. i.e. There will be a final result where the recursion can stop. Otherwise, recursion will continue forever. So make sure you write it’s bottom out.

### Note

A recursive function must contain at least one non-recursive branch.

The recursive calls must eventually lead to non-recursive branch.

5. Make a main function

6. Make initialize and declare an integer.

7. Call the factorial function in the main and pass the integer.

8. Be a fancy programmer and print the returned result neatly

And there you have it. You’re first recursive program. Practice this and other questions.

### Points to keep in mind

- If we use iteration, we must be careful not to create an infinite loop by accident
- If we use recursion we must be careful not to create an infinite chain of function calls
- Always make sure that the recursion bottoms out

### About Joudet Ahsan

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