ansi_c_pg059_ch03_ex06.c

/*
 * Exercise 3-6.
 * Write a version of itoa that accepts three arguments instead of two. The
 * third argument is a minimum field width; the converted number must be padded
 * with blanks on the left if necessary to make it wide enough.
 */

#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 w)
{
	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++] = '-';

	while (w > i)
		s[i++] = ' ';

	s[i] = '\0';
	reverse(s);
}

int
main(int argc, char **argv)
{
	char s[100];
	itoa(2147483648, s, 30);
	printf("\"%s\"\n", s);
	return (0);
}