1 /*
2  * Exercise 3-4. In a two's complement number representation, our version of
3  * itoa does not handle the largest negative number, that is, the value of n
4  * equal to -(2^(wordsize-1)). Explain why not. Modify it to print that value
5  * correctly, regardless of the machine on which it runs.
6  */
7 
8 /* In the step n = -n, it is not possible to negate the largest negative
9  * number without integer overflow.
10  */
11 
12 #include <string.h>
13 #include <stdio.h>
14 #include <limits.h>
15 
16 void reverse(char s[]) {
17 	int c, i, j;
18 	for (i = 0, j = strlen(s)-1; i<j; i++, j--) {
19 		c = s[i];
20 		s[i] = s[j];
21 		s[j] = c;
22 	}
23 }
24 
25 void itoa(int n, char s[]) {
26 	int i, sign;
27 	unsigned u;
28 	if ((sign = n) < 0)
29 		u = -n;
30 	i = 0;
31 	do {
32 		s[i++] = u % 10 + '0';
33 	} while ((u /= 10) > 0);
34 	if (sign < 0)
35 		s[i++] = '-';
36 	s[i] = '\0';
37 	reverse(s);
38 }
39 
40 int main() {
41 	/* word size is 32 bits */
42 	char s[100];
43 	int i = -147483648;
44 	itoa(i, s);
45 	printf("Actual: %s\n", s);
46 	printf("Expect: %s\n", "-147483648");
47 	i = INT_MIN+1;
48 	itoa(i, s);
49 	printf("Actual: %s\n", s);
50 	printf("Expect: %d\n", INT_MIN+1);
51 	i = INT_MIN;
52 	itoa(i, s);
53 	printf("Actual: %s\n", s);
54 	printf("Expect: %d\n", INT_MIN);
55 	return 0;
56 }