Recursion Function

[t2nator]

I've looked at some tutorials online but I still can't figure out how this is evaluating to 341. If the first value is 4 and is passed to the function then the first if is true so it returns 4-1 * 4 + 1, that's all I can get from this.

#include <iostream>
using namespace std;
int tryit(int i)
{
int j=4;
int k=1;
        if(i > 0)
          return tryit(i-1) * j + k;
        else
          return 1;
}
int main()
{
int i = 4;
int x;
x =  tryit(i);
cout << "x= " << x << endl;
return 0;
}

[ModShop]

"Run" your program on paper. Until tryit(0) is called, it keeps calling itself. Look at this little stack trace I made.

tryit(0) = 1
tryit(1) = (1) * 4 + 1 = 5
tryit(2) = (5) * 4 + 1 = 21
tryit(3) = (21) * 4 + 1 = 85
tryit(4) = (85) * 4 + 1 = 341

The numbers in parenthesis are the return values of the recursive call to tryit(). What exactly are you trying to do?

[t2nator]

this is a sample question for my exam, but we did not do anything with recursion during the semester. I think what was confusing me was the tryit(i - 1)

[t2nator]

I thought the return 1 was to break the loop after once i = 0?

[ModShop]

Once i = 0, it stops calling itself (that is why there is no tryit(-1) being called), but still has to go back up the stack and finish all the other calls to tryit().