What is the output of this and how?

Question

int foo(int x){
if(x<=1)
return 1;
return foo(x-1)*x;
}
int main(){
cout<<foo(4);
}

Answer 1

This will return 4! = 24

This is an example of recursive function, which means that it calls itself.

So here is how that works:

Foo(4) is called from main
Foo(3) is called from Foo(4)
Foo(2) is called from Foo(3)
Foo(1) is called from Foo(2)
In Foo(1) X==1 so that function returns 1 back to foo(2)
Then foo(2) returns 1*2=2 to foo(3)
Foo(3) returns 2*3=6 to foo(4)
Foo(4) returns 6*4=24 back to main function where it gets printed.

Answer 2

It's like doing (3 x 2 x 1) x 4

When the recursion base case is reached (<x> <= 1) it returns 1.

Before it did, it does multiplication of number sequence - 3 then 2

Recursion is indeed tricky to explain though. Hope I wasn't mistaken ...

Answer 3

Ok thank u for the explanation 👍