ansi_c_pg059_ch03_ex04.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
 * -(2wordsize-1). Explain why not.Modify it to print that value correctly,
 * regardless of the machine on which it runs.
 */



/*
 * 2^31 = 0x8000 =
 * 10000000000000000000000000000000
 * when extecuting n =-n it results to the same number, and n remains negative
 * number. n%10 is reults in a negative number in that case.
 */


#include <stdio.h>
#include <string.h>
/* 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;
	}
}


void
itoa(int n, char s[])
{
	int i, sign;
	unsigned int un = n;
	if ((sign = n) < 0)	/* record sign */
		un = -n;		/* make n positive */
	i = 0;
	do {			/* generate digits in reverse order */
		s[i++] = un % 10 + '0';	/* getnextdigit */
	} while ((un /= 10) > 0);
	if (sign < 0)
		s[i++] = '-';
	s[i] = '\0';
	reverse(s);
}

int
main(int argc, char **argv)
{
	char s[100];
	itoa(2147483648, s);
	printf("%s\n", s);
	return (0);
}