Hello friends and welcome to GeeksforGeeks.

In this video, we’ll see C program for factorial of a number.

Factorial of a non-negative integer n is the multiplication of all positive integers smaller

than or equal to n. i.e. n! is equal to the product

of n, n-1, n-2 and so on up till 1. For e.g., 4! is equal to 4*3*2*1 which is 24. Similarly, 6!

Will be 6*5*4*3*2*1 which is 720. One way to find the factorial of a number

is using recursion. Now, n! can be written as n * (n-1)!. This is so because (n-1)! includes

all the terms from n-1 * n-2 up till 1. Note that 0! and 1! are both 1. To find the factorial of

a number, we call this recursive function factorial. Now, our base case is n=0, which should return

1. For any other n, we return n*factorial(n-1) because as said earlier (n-1)! includes all

terms from n-1 up till 1 multiplied with each other. This is how n! gets calculated using method

of recursion. Now the 2 nd solution we’ll be seeing is

iterative one. Variable res is initially 1 and it will be storing the factorial of the number. Now,

we know that n! is n* n-1*n- 2 and so on till 1. That’s what we are doing here. i goes on

from 2 to n and all the numbers between 2 to n get multiplied and stored in res. This is how

simple the iterative solution is. The time complexity of both the solutions

is O(n). Thank you for watching the video. Please leave

us your comments.

can you also add the working program in this video

https://youtu.be/Adi16Sa85c0