Exercise3-4.c

/*Exercise 3-4. In a two's complement number representation,
our version of itoa does not handle the largest negative number,
that is, the value of n equal to -(2^(wordsize-1)) Explain why not.
Modify it to print that value correctly, regardless of the machine
on which it runs.

It does not handle the largest negative number because it 
does not have a positive equivalent; -n where n is the largest
negative number gives n; because n is still negative n%10 gives
negative values instead of the desired positive ones. If we take 
the absolute value of n%10 we get the correct value and character*/

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <limits.h>

void itoa(int n, char s[]);
void reverse(char s[]);

int main(void)
{
    int n = INT_MIN;
    char s[16];

    itoa(1337, s);
    printf("%s\n", s);
    itoa(n, s);
    printf("%s\n", s);

    return EXIT_SUCCESS;
}

/* itoa:  convert n to characters in s */
void itoa(int n, char s[])
{
    int i, sign;

    sign = n;
    i = 0;
    do {        /* generate digits in reverse order */
        s[i++] = abs(n % 10) + '0';     /* get next digit */
    } while (n /= 10);                  /* delete it */
    if (sign < 0)
        s[i++] = '-';
    s[i] = '\0';
    reverse(s);
}

/* reverse:  reverse string s in place */
void reverse(char s[])
{
    int c, i, j;

    for (i = 0, j = strlen(s)-1; i < j; i++, j--) {
        c = s[i];
        s[i] = s[j];
        s[j] = c;
    }
}