Thread: Recursive Trace

I really need help learning how to get the output of this program.. I'm not completely lost but I need it in the simplest terms. I have a test soon and I'm trying to study.

Code:

/*Recursive Trace
   Written by Ron
   April 2006
*/

#include <stdio.h>


int barph(int a[5], int upchuck);


int main(void)
{int a[5]={11, 13, 15, 17, 19};
int krud;
krud=0;
krud=krud*barph(a,3);
printf("final result is %d\n", krud);
return 0;
}


int barph(int a[5], int upchuck)
{int sick;
sick=1;
if (upchuck>1)
        sick=a[upchuck]+barph(a,upchuck-1)+3;
printf("upchuck is %d, sick is %d\n", upchuck, sick);
return(sick);
}

It prints out:

upchuck is 1, sick is 1
upchuck is 2, sick is 19
upchuck is 3, sick is 39
final result is 0

Have you sat down with a piece of paper and traced out the values of the variables? If so, where did you get stuck?

I get stuck where on the sick=a[upchuck]+barph(a,upchuck-1)+3;
because I don't understand how to figure out the value of barph and get the answer 19.

You know what the values of a and upchuck-1 are at this point, so go through the function (again!) with those numbers.

I'm not so sure I really do though.. is "a" 17 and is "upchuck-1" 2? What do I do with those numbers multiply them? How does that get 19? I guess that's where I'm lost.

You call the function again. So you start back up at line 22, but now upchuck is 2, since that was the value of the second parameter

I got that part. How do I put these numbers together to get 19?

Originally Posted by Kim Valentin

I got that part. How do I put these numbers together to get 19?

You don't.

You need to keep going. Go back to line 22 and start again. When you get to line 26 the second time, you will have another function call, and you will go back (again) to line 22 and start (yet) again. When you see the function call "barph( , )" you have to do that function call to figure out what that value is -- it's not an immediate thing.

I'm still lost as ever but thanks for trying.