would't this recursion run forever?-CodePudding

So I come across this simple lines of code from a tutorial on YouTube. It's about recursion.

public class whatever{

  public static void main (string[] args){
    factorial(7);
  }  
  private static int factorial(int num){
    if(num<1) return 1;
    return num * factorial(num -1);
  }


}

Wouldn't it run forever because once the num reaches 0, it will return 1, then it will be -1, still return 1, then -2, return 1? please correct me.

I know I am probably wrong logically so please correct me.

CodePudding user response：

this line would ensure that the flow doesnt continue to infinity: if(num<1) return 1; once the factorial method is called with 0 as num, return 1 would stop any furture calls to the factorial method, and the control goes back to the main method and exits from there on.

CodePudding user response：

It does not go to infinity - once you get down to calling factorial(0) you return with 1 and don't call any method.

    f(7) = n * f(6)
n * f(6) = n * n-1 * f(5)
       .....
    f(7) = n * n-1 * n-2 * ... * n-6   1