1 /*
2  * Exercise 3-3. Write a function expand(s1, s2) that expands shorthand
3  * notations like a-z in the string s1 into the equivalent complete list
4  * abc...xyz in s2. Allow for letters of either case and digits, and be
5  * prepared to handle cases like a-b-c and a-z0-9 and -a-z. Arrange that
6  * a leading or trailing - is taken literally.
7  */
8 
9 #include <stdio.h>
10 
11 int expand(char *s1, char *s2);
12 
13 int main()
14 {
15 	char expansion[200];
16 	expand("a-z", expansion);
17 	printf("Expect: abcdefghijlkmnopqrstuvwxyz\n");
18 	printf("Result: %s\n", expansion);
19 	expand("A-Z", expansion);
20 	printf("Expect: ABCDEFGHIJLKMNOPQRSTUVWXYZ\n");
21 	printf("Result: %s\n", expansion);
22 	expand("0-9", expansion);
23 	printf("Expect: 0123456789\n");
24 	printf("Result: %s\n", expansion);
25 	expand("a-z0-9", expansion);
26 	printf("Expect: abcdefghijlkmnopqrstuvwxyz0123456789\n");
27 	printf("Result: %s\n", expansion);
28 	expand("-a-z", expansion);
29 	printf("Expect: -abcdefghijlkmnopqrstuvwxyz\n");
30 	printf("Result: %s\n", expansion);
31 	expand("a-b-c", expansion);
32 	printf("Expect: abc\n");
33 	printf("Result: %s\n", expansion);
34 	return 0;
35 }
36 
37 /* return value is number of expansions */
38 int expand(char *s1, char *s2) {
39 	int expansions = 0;
40 	char prev = '\0';
41 	char next;
42 	while (*s1) {
43 		if (*s1 == '-') {
44 			next = *(s1+1);
45 			if ((prev >= 'a' && next <= 'z') ||
46 				(prev >= 'A' && next <= 'Z') ||
47 				(prev >= '0' && next <= '9')) {
48 				prev++; /* first letter copied by default */
49 				expansions++;
50 				while (prev < next) { /* last letter copied by default */
51 					*s2++ = prev++;
52 				}
53 				s1++;
54 			}
55 		}
56 		prev = *s2++ = *s1++;
57 	}
58 	*s2 = '\0';
59 	return expansions;
60 }