C++ questio about functions

dror's Avatar, Join Date: Dec 2011
Newbie Member
hello i wrote this short program that need just to multyply between 2 numbers ,but doing so only by useing + (thats our assigment from class)
the program do the work but it also add numbers like 449176 why does it do it ??,i feel that the answer will make me understand function real better ,any one know the answer??
Code:
 
#include <iostream.h>
int kefel(int A,int B);
int kefel(int A,int B)
{
int x,y,t=0;
    for (x=0;x<A;x++)
    {
        for (y=0;y<B;y++)
        {
           t=++t;
            }
            }
   cout<<t;
}
  int main()          
{
int a=0,b=0,k=0;
cin>>a>>b;
  cout<<kefel (a,b);
        cin>>k;
            return 0;
                  }

Last edited by shabbir; 14Dec2011 at 21:59.. Reason: Code blocks
0
Scripting's Avatar, Join Date: Jun 2010
John Hoder
I don't understand the function enough to help you, but I can give you one little advice : instead of using "cin>>k" use "cout<<endl; system("PAUSE");"
0
xpi0t0s's Avatar, Join Date: Aug 2004
Mentor
Undefined behaviour
Code:
t=++t;
If you want to increment t, use ONE of the following, and DO NOT try to mix them:
Code:
t++;
++t;
t=t+1;
By the way, your program might work, but it doesn't use +. It uses ++, which is not the same.
You can do multiplication with repeated addition, e.g. 3*6=6+6+6 - that's 6 added to a zero-initialised accumulator 3 times.
0
Chong's Avatar, Join Date: May 2011
Go4Expert Member
Hi your keffel() functions is supposed to return int. The program as it is won't compile.
Bestt regards
Chong
0
Scripting's Avatar, Join Date: Jun 2010
John Hoder
Quote:
Originally Posted by Chong View Post
Hi your keffel() functions is supposed to return int. The program as it is won't compile.
Bestt regards
Chong
IMHO, it can be compiled without any difficulties ...
0
xpi0t0s's Avatar, Join Date: Aug 2004
Mentor
Good point; I hadn't spotted that.

kefel() doesn't actually return a value to the calling function (main). However it does display the value of t before it returns. So (if t=++t does what the OP thinks, i.e. t=t+1) it will display the correct value.

What happens after the function returns, on the "cout<<kefel (a,b);" line, depends on the compiler's method of returning values. For Microsoft Visual Studio on Windows, it is the value in the EAX register. Since there is no "return" statement, the value "returned" will effectively be whatever junk was in EAX (however, MSVS would throw an error, preventing compilation, due to the lack of the return value). This could account for the "numbers like 449176" observed by the OP.

If the OP is using a very old compiler then it is possible it does not enforce the "non-void function must return a value" rule.