Page 64

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` to the power `(wordsize - 1))`. Explain why not. Modify it to print that value correctly regardless of the machine on which it runs.

``````#include <stdbool.h>
#include <limits.h>
#include <stdio.h>
#include <string.h>

#define LEN 1000

/* The solution involves an implementation of itoa that doesn't require negative numbers
* to be flipped to positive, as this will never work. */

void itoa(int n, char s[]);
void itoa2(int n, char s[]);
void reverse(char s[]);

int main()
{
char s[LEN];

itoa2(-1234, s);

printf("%s", s);
}

void itoa2(int n, char s[])
{
int i, sign;
sign = n < 0 ? -1 : 1;

i = 0;
do {
s[i++] = (n % 10 * sign) + '0';
} while ((n /= 10) != 0);
if (sign < 0)
s[i++] = '-';
s[i] = '\0';
reverse(s);
}

void itoa(int n, char s[])
{
int i, sign;

if ((sign = n) < 0)
n = -n;
i = 0;
do {
s[i++] = n % 10 + '0';
} while ((n /= 10) > 0);
if (sign < 0)
s[i++] = '-';
s[i] = '\0';
reverse(s);
}

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;
}
}
``````