query about recursion function

using System;
namespace InterviewQuestionPart4
{
class Program
{
static void Main(string[] args)
{
Console.WriteLine("Please Enter a Number");
//read number from user
int number =Convert.ToInt32(Console.ReadLine());
//invoke the static method
double factorial = Factorial(number);
//print the factorial result
Console.WriteLine("factorial of"+number+"="+factorial.ToString());
}
public static double Factorial(int number)
{
if (number == 0)
return 1;
return number * Factorial(number-1);//Recursive call
}
}
}

in the above program when condition is satisfied then its should return 1as output then how the result is return?

The q is returned when the last recursive call is reached, at that time the returned 1 is multiplied with the number variable from the previous call stack and keeps going to multiply until the recursion whole stack is executed.

For example, user input 5 as numbers, then the call would be like:

return 5 * Factorial(5-1);// this will cause to call Factorial method again
return 4 * Factorial(4-1); // this will cause to call Factorial method again
return 3 * Factorial(3-1); // this will cause to call Factorial method again
return 2 * Factorial(2-1); // this will cause to call Factorial method again
return 1; // this will cause to call Factorial method again

Now the recursive call will be backtracked so 1 is returned from last recursive call which is then multiple with previous stack call which will be 2*1 and then result will be returned to the call previous than this which will be 3*2 and this will go on until the first call is reached which return 5 * Factorial(5-1) and the end result will be returned to the Console.WriteLine call parameter.

I hope it helps you.

1 Reply

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Ehsan Sajjad10y ago
Accepted answer
The q is returned when the last recursive call is reached, at that time the returned 1 is multiplied with the number variable from the previous call stack and keeps going to multiply until the recursion whole stack is executed.
For example, user input 5 as numbers, then the call would be like:
return 5 * Factorial(5-1);// this will cause to call Factorial method again
return 4 * Factorial(4-1); // this will cause to call Factorial method again
return 3 * Factorial(3-1); // this will cause to call Factorial method again
return 2 * Factorial(2-1); // this will cause to call Factorial method again
return 1; // this will cause to call Factorial method again
Now the recursive call will be backtracked so 1 is returned from last recursive call which is then multiple with previous stack call which will be 2*1 and then result will be returned to the call previous than this which will be 3*2 and this will go on until the first call is reached which return 5 * Factorial(5-1) and the end result will be returned to the Console.WriteLine call parameter.
I hope it helps you.