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#include <stdio.h>
#include <ctype.h>
/* The C Programming Language: 2nd Edition
*
* Exercise 3-3: Write a function expand(s1,s2) that expands shorthand
* notations like 'a-z' in the string s1 into the equivalent complete list
* 'abc...xyz' in s2. Allow for letters of either case and digits, and be
* prepared to handle cases like 'a-b-c' and 'a-z0-9' and '-a-z'. Arrange that
* a leading or trailing '-' is taken literally.
*
* Answer: This one was fun. The trick is to target dashes, since they have the
* special behavior. From there, you decide what to do based on context. Once
* you've determined that the characters on both sides of the dash are letters
* OR numbers - no mixing - you store both values and put'em through a loop to
* output the range. There are a few edge cases to watch out for, but it's
* pretty simple to account for them.
*
* A limitation of my expand() is leading and trailing dashes are only output
* once. You can lead or trail with > 1 dash and it will truncate it to only 1.
* This could be seen as a bug or a feature. I haven't decided.
*/
void expand(char s1[], char s2[]) {
int i, j;
char start = 0;
char end = 0;
for (i = 0, j = 0; s1[i] != '\0'; i++) {
if (s1[i] == '-') {
if ((isalpha(s1[i - 1]) && isalpha(s1[i + 1])) || (isdigit(s1[i - 1]) && isdigit(s1[i + 1]))) {
start = s1[i - 1];
end = s1[i + 1];
start = tolower(start);
end = tolower(end);
if (start == s2[j - 1]) {
start++;
}
while (start <= end) {
s2[j++] = start++;
}
} else {
if (i == 0 || s1[i + 1] == '\0') {
s2[j++] = '-';
}
}
}
}
s2[j] = '\0';
}
int main() {
char foo[21] = "A-Z";
char bar[21] = "0-9";
char baz[21] = "A-g-N";
char fob[21] = "2-5-9";
char woot[21] = "-a-f0-36-9b-h-";
char derp[21] = "a-28-t";
char dest[61] = "";
printf("%26s\n", "INPUT | OUTPUT");
printf("%27s\n", "-----------------");
expand(foo, dest);
printf("%16s => %s\n", foo, dest);
expand(bar, dest);
printf("%16s => %s\n", bar, dest);
expand(baz, dest);
printf("%16s => %s\n", baz, dest);
expand(fob, dest);
printf("%16s => %s\n", fob, dest);
expand(woot, dest);
printf("%16s => %s\n", woot, dest);
expand(derp, dest);
printf("%16s => %s\n", derp, dest);
return 0;
}
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