Is it bad to underflow then overflow an unsigned variable?

Question

Kraaa.

I am a student in a programming school who requires us to write C functions with less than 25 lines of code. So, basically, every line counts. Sometimes, I have the need to shorten assignments like so:

#include <stddef.h>
#include <stdio.h>

#define ARRAY_SIZE  3

int     main(void)
{
    int     nbr_array[ARRAY_SIZE] = { 1, 2, 3 };
    size_t  i;

    i = -1;
    while (++i < ARRAY_SIZE)
        printf("nbr_array[%zu] = %i\n", i, nbr_array[i]);
    return (0);
}

The important part of this code is the size_t counter named i. In order to save up several lines of code, I would like to pre-increment it in the loop's condition. But, insofar as the C standard defines size_t as an unsigned type, what I am basically doing here, is underflowing the i variable (from 0 to a very big value), then overflowing it once (from that big value to 0).

My question is the following: regardless of the bad practises of having to shorten our code, is it safe to set an unsigned (size_t) variable to -1 then pre-increment it at each iteration to browse an array?

Thanks!

Answer 1

The i = -1; part of your program is fine.

Converting -1 to an unsigned integer type is defined in C, and results in a value that, if incremented, results in zero.

This said, you are not gaining any line of code with respect to the idiomatic for (i=0; i<ARRAY_SIZE; i++) ….

Your %zi format should probably be %zu.