練習3.3

#include <stdio.h>
#include <stdlib.h>

#define MAX_LENGTH 1000

void expand(char *s1, char *s2);

int main(int argc, char *argv[])
{
    char s1[MAX_LENGTH] = "a-f abcde 0-9";
    char s2[MAX_LENGTH] = "";
    expand(s1, s2);
    printf("%s", s2);
    return 0;
}


void expand(char *s1, char *s2)
{
    size_t j = 0;
    for (size_t i = 0; s1[i] != '\0'; ++i) {

        if (s1[i] == '-') {
            for (char c = s1[i-1]+1; c <= s1[i+1]; ++c) {
                s2[j++] = c;
            }
            ++i;
        } else {
            s2[j++] = s1[i];
        } 
    }
    s2[j++] = '\0';
}