it crashes but it should print 8 to the screen. Its under my nose but I don't know why.Code:# include <stdio.h> // if num = 5 print 4*2=8 // if num = 6 print 6*4*2 = 48 int even_prod(int num) { if (num%2 != 0) return (even_prod(num-1)); else return (num *(even_prod(num-2))); } int main() { printf("%d\n", even_prod(5)); return 0; }
Try using a debugger or adding some useful debugging output to see what's going on:
That should give you a huge clue.Code:int even_prod(int num) { printf("num = %d\n", num); if (num%2 != 0) return (even_prod(num-1)); else return (num *(even_prod(num-2))); }
You never return to main. In all cases you call the function recursively and eventually you run out of stack space.
A recursive function has a general form of
Code:foo( ) { if( base-case ) return something/nothing else recursive-call }
Last edited by Tclausex; 02-15-2013 at 01:53 PM. Reason: code gernerality
Indeed, it is recursive on all control paths. I've actually seen a compiler warning about that once.
My homepage
Advice: Take only as directed - If symptoms persist, please see your debugger
Linus Torvalds: "But it clearly is the only right way. The fact that everybody else does it some other way only means that they are wrong"
Add this condition to your program:
Code:int even_prod(int num) { if(num!=0) { if (num%2 != 0) return (even_prod(num-1)); else return (num *(even_prod(num-2))); } } int main() { printf("%d\n", even_prod(5)); return 0; }
Close, but not quite:Originally Posted by eramit2010
You need to return something in the case that num is zero. Since it's a product function, the multiplicative identity (1) is a good choice.Code:$ cat prod.c #include <stdio.h> int even_prod(int num) { if(num!=0) { if (num%2 != 0) return (even_prod(num-1)); else return (num *(even_prod(num-2))); } } int main() { printf("%d\n", even_prod(5)); return 0; } $ make prod gcc -Wall -Wunreachable-code -ggdb3 -std=c99 -pedantic -lm -lpthread prod.c -o prod prod.c: In function ‘even_prod’: prod.c:11: warning: control reaches end of non-void function
