Finding factorial by recursion

As I have discussed in my previous blog that a function that repeats itself is called recursion.So, today I am here with  a very common example of recursion in C++. In this example, I will find the factorial of a given number by recursion.Below is the source code of this program.

Source code

1. #include <iostream>
2. using namespace std;
3. 
   
4. int factorial(int);
5. 
   
6. int main() {
7.     int n;
8.     cout<<"Enter a number: ";
9.     cin>>n;
10.     cout<<"Factorial="<<factorial(n);
11.     return 0;
12. }
13. 
    
14. int factorial(int n) {
15.     if (n>1) {
16.         return n*factorial(n-1);
17.     }
18.     else {
19.         return 1;
20.     }
21. }

Output

Explanation

Suppose user enters 4 which is passed to function factorial(). Here are the steps involved:

• In first factorial() function, test expression inside if statement is true. The statement return num*factorial(num-1); is executed, which calls second factorial() function and argument passed is num-1 which is 3.
• In second factorial() function, test expression inside if statement is true. The statementreturn num*factorial(num-1); is executed, which calls third factorial() function and argument passed is num-1 which is 2.
• In third factorial() function, test expression inside if statement is true. The statement return num*factorial(num-1); is executed, which calls fourth factorial() function and argument passed is num-1 which is 1.
• The fourth factorial() function, test expression inside if statement is false. The statementreturn 1; is executed, which returns 1 to third factorial() function.
• The thrid factorial() function returns 2 to second factorial() function.
• The second factorial() function returns 6 to first factorial() function.
• Finally, first factorial() function returns 24 to the main() function and is displayed.        ( The above reference has been taken from www.programiz.com)