Debugging GDB

[Ducol]

Hello!

I am learning debugging with gdb. I have found this video on youtube
http://www.youtube.com/watch?v=bAZTd769y8E

Following the example, I am trying to run debugger, but it doesn't display a for loop.
These are my steps from the Terminal:

(gdb) l
10        d = -1;
11        
12        for (; d <= (TOTAL_ELEMENTS - 2); d++)
13            printf("%d\n", array [d + 1]);
14        
15        return 0;
16    }
(gdb) break main
Note: breakpoint 1 (disabled) also set at pc 0x100000e74.
Breakpoint 2 at 0x100000e74: file debug1.c, line 7.
(gdb) r
Starting program: /Users/Alla/CS50/TextBook/kandr/exercises/debug1 

Breakpoint 2, main () at debug1.c:7
7        int array[] = {23, 34, 12, 17, 204, 99, 16};
(gdb) n
10        d = -1;
(gdb) n
15        return 0;
(gdb)

Here is the intentionally buggy program (example from youtube
video):

#include <stdio.h>

#define TOTAL_ELEMENTS (sizeof(array) / sizeof(array[0]))

int main(void)
{
    int array[] = {23, 34, 12, 17, 204, 99, 16};
    
    int d;
    d = -1;
    
    for (; d <= (TOTAL_ELEMENTS - 2); d++)
        printf("%d\n", array [d + 1]);
    
    return 0;
}

Please, help me to understand why I get to line 15 return 0 instead
of line 12 which is a for loop?
Thank you!

[laserlight]

The type of result of sizeof is size_t, an unsigned integer type. Hence in the expression d <= (TOTAL_ELEMENTS - 2), (TOTAL_ELEMENTS - 2) is of type size_t because 2 is converted to size_t, assuming that the rank of size_t is greater than or equal to the rank of int, hence the entire expression is of type size_t because d is likewise converted to size_t. Since d == -1, it is converted to a large unsigned integer, and this unsigned integer is greater than (TOTAL_ELEMENTS - 2).

[Ducol]

The type of result of sizeof is size_t, an unsigned integer type. Hence in the expression d <= (TOTAL_ELEMENTS - 2), (TOTAL_ELEMENTS - 2) is of type size_t because 2 is converted to size_t, assuming that the rank of size_t is greater than or equal to the rank of int, hence the entire expression is of type size_t because d is likewise converted to size_t. Since d == -1, it is converted to a large unsigned integer, and this unsigned integer is greater than (TOTAL_ELEMENTS - 2).

Thank you very much for this helpful explanation.