ansi_c_pg059_ch03_ex05.c

/*
 * Exercise 3-5.
 * Write the function itob(n,s,b) that converts the integer n into a base b
 * character representation in the string s. In particular, itob(n,s,16)
 * formats s as a hexadecimal integer in s.
 */



#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[],unsigned int b)
{
	int i, sign;
	unsigned int un = n;
	char c;
	if ((sign = n) < 0)	/* record sign */
		un = -n;		/* make n positive */
	i = 0;
	do {
		if ((c = (un % b)) <= 9) {
			c = c + '0';
		} else {
			c = c - 10 + 'a';
		}

		s[i++] = c;	/* getnextdigit */
	} while ((un /= b) > 0);
	if (sign < 0)
		s[i++] = '-';
	s[i] = '\0';
	reverse(s);
}

int
main(int argc, char **argv)
{
	char s[100];
	itoa(108, s, 16);
	printf("%s\n", s);
	return (0);
}