loop problem

[fattaneh]

hi all ,
i have written this code , and it should be in while if num is not
zero
so it shouldn't print error , but num becomes zero and it wont come
out of while
i have written this code in visual studio c++

#include "stdafx.h"
#include <stdio.h>
using namespace System;

int main(array<System::String ^> ^args)
{
int num =5 ;
while (num !=0)
{
num-- ;
if(num ==0)
{
printf("error") ; // it should never write this but it
will write .
}
}
return 0;
}


could you help me to filnd out what the problem is ?

thanks of all . . .

 

[fattaneh]

The while condition is only tested once at the start of each iteration
of the loop; it is not tested after every statement inside the loop.

/Leigh

Thank you

 

[Markus Wichmann]

hi all ,
i have written this code , and it should be in while if num is not
zero
so it shouldn't print error , but num becomes zero and it wont come
out of while
i have written this code in visual studio c++

#include "stdafx.h"

Doesn't look much like standard...

#include <stdio.h>
using namespace System;

int main(array<System::String ^> ^args)

^^^^^^^^^^^^^^^^^^^^^^^^^
Definitely _not_ standard. The standard is one of:

int main()
int main(int argc, char* argv[])

or equivalent. (There are two other forms for argv that mean exactly the
same.)

{
int num =5 ;
while (num !=0)
{
num-- ;
if(num ==0)
{
printf("error") ; // it should never write this but it
will write .
}
}
return 0;
}


could you help me to filnd out what the problem is ?

thanks of all . . .

Short: Move the decrement instruction to the other side of the loop!

Long: The condition of a while-loop is checked only on entry and on
repeat, not after every instruction inside the loop. Thus, if num is 1
at the beginning of the loop, it is decremented to 0, then the if fires.

HTH,
Markus