1 5dc21454 2023-07-14 jrmu /*
 2 5dc21454 2023-07-14 jrmu  * Exercise 3-4. In a two's complement number representation, our version of
 3 5dc21454 2023-07-14 jrmu  * itoa does not handle the largest negative number, that is, the value of n
 4 5dc21454 2023-07-14 jrmu  * equal to -(2^(wordsize-1)). Explain why not. Modify it to print that value
 5 5dc21454 2023-07-14 jrmu  * correctly, regardless of the machine on which it runs.
 6 5dc21454 2023-07-14 jrmu  */
 7 5dc21454 2023-07-14 jrmu 
 8 5dc21454 2023-07-14 jrmu /* In the step n = -n, it is not possible to negate the largest negative
 9 5dc21454 2023-07-14 jrmu  * number without integer overflow.
10 5dc21454 2023-07-14 jrmu  */
11 5dc21454 2023-07-14 jrmu 
12 5dc21454 2023-07-14 jrmu #include <string.h>
13 5dc21454 2023-07-14 jrmu #include <stdio.h>
14 5dc21454 2023-07-14 jrmu #include <limits.h>
15 5dc21454 2023-07-14 jrmu 
16 5dc21454 2023-07-14 jrmu void reverse(char s[]) {
17 5dc21454 2023-07-14 jrmu 	int c, i, j;
18 5dc21454 2023-07-14 jrmu 	for (i = 0, j = strlen(s)-1; i<j; i++, j--) {
19 5dc21454 2023-07-14 jrmu 		c = s[i];
20 5dc21454 2023-07-14 jrmu 		s[i] = s[j];
21 5dc21454 2023-07-14 jrmu 		s[j] = c;
22 5dc21454 2023-07-14 jrmu 	}
23 5dc21454 2023-07-14 jrmu }
24 5dc21454 2023-07-14 jrmu 
25 5dc21454 2023-07-14 jrmu void itoa(int n, char s[]) {
26 5dc21454 2023-07-14 jrmu 	int i, sign;
27 5dc21454 2023-07-14 jrmu 	unsigned u;
28 5dc21454 2023-07-14 jrmu 	if ((sign = n) < 0)
29 5dc21454 2023-07-14 jrmu 		u = -n;
30 5dc21454 2023-07-14 jrmu 	i = 0;
31 5dc21454 2023-07-14 jrmu 	do {
32 5dc21454 2023-07-14 jrmu 		s[i++] = u % 10 + '0';
33 5dc21454 2023-07-14 jrmu 	} while ((u /= 10) > 0);
34 5dc21454 2023-07-14 jrmu 	if (sign < 0)
35 5dc21454 2023-07-14 jrmu 		s[i++] = '-';
36 5dc21454 2023-07-14 jrmu 	s[i] = '\0';
37 5dc21454 2023-07-14 jrmu 	reverse(s);
38 5dc21454 2023-07-14 jrmu }
39 5dc21454 2023-07-14 jrmu 
40 5dc21454 2023-07-14 jrmu int main() {
41 5dc21454 2023-07-14 jrmu 	/* word size is 32 bits */
42 5dc21454 2023-07-14 jrmu 	char s[100];
43 5dc21454 2023-07-14 jrmu 	int i = -147483648;
44 5dc21454 2023-07-14 jrmu 	itoa(i, s);
45 5dc21454 2023-07-14 jrmu 	printf("Actual: %s\n", s);
46 5dc21454 2023-07-14 jrmu 	printf("Expect: %s\n", "-147483648");
47 5dc21454 2023-07-14 jrmu 	i = INT_MIN+1;
48 5dc21454 2023-07-14 jrmu 	itoa(i, s);
49 5dc21454 2023-07-14 jrmu 	printf("Actual: %s\n", s);
50 5dc21454 2023-07-14 jrmu 	printf("Expect: %d\n", INT_MIN+1);
51 5dc21454 2023-07-14 jrmu 	i = INT_MIN;
52 5dc21454 2023-07-14 jrmu 	itoa(i, s);
53 5dc21454 2023-07-14 jrmu 	printf("Actual: %s\n", s);
54 5dc21454 2023-07-14 jrmu 	printf("Expect: %d\n", INT_MIN);
55 5dc21454 2023-07-14 jrmu 	return 0;
56 5dc21454 2023-07-14 jrmu }