Question

Possible Duplicate:
Turbo C Array Question

#include <stdio.h>

#define LIM 40

int main()
{
       int day=0;
       float temp[LIM];
       do
       {
               printf("Enter temperature for day %d.", day);
               scanf("%f", &temp[day]);
       }
       while(temp[day++] && day<LIM );
}

About the last line. Why is it not satisfied with while(temp[day++] > 0)? since I have set the LIM with the value of 40? Why should I add some additional condition, like day<LIM?

Answer 1

Because, if you enter 41 numbers, you will write to a location outside the array, invoking the dreaded undefined behaviour. When you attempt to write to temp[40] (the 41st element), you’ll likely clobber memory that you shouldn’t. It may work for a little bit beyond the end of the array but that’s the nature of undefined behaviour. It’s still not a good idea.

The day < LIM bit will force the loop to exit when you’ve entered 40 temperatures, regardless of what value you’ve actually entered.