/*******************************************************************************
 *
 * K&R exercise 3-3
 * expand - when it appears between lists such as a-z A-Z and 1-9. Ignore all 
 * illogical expansions and print "-" when it appears in such cases.
 *
 * program: expand
 * by.....: yetimach
 * date...: 4 November 2024
 *
 * ****************************************************************************/

#include <stdio.h>
#include <ctype.h>
#include <string.h>

#define MAX 100 

char gs1[MAX]; /* global string */
char gs2[MAX]; /* global string */

void expand(char s1[], char s2[]){
    int i, j, c, nc, sc, ec; /* new char, start char, end char */
    i = j = 0;
    int add = 1;
    while ((c = s1[i++]) != '\0' && i < MAX-1 && j < MAX-1){
        if (c != '-')
            s2[j++] = c;
        else{
            if (i-1 != 0){
                sc = s1[i-2];
                ec = s1[i];
                if (((isalpha(sc) && isalpha(ec)) || (isdigit(sc) 
                                && isdigit(ec))) && (sc < ec)){
                    while ((nc = sc + add++) < ec && c != '\0' && i < MAX-1 &&
                            j < MAX-1)
                        s2[j++] = nc;
                    add = 1;
                }
            }else
                s2[j++] = c;
        }
    }
    s2[j] = '\0';
    return;
}

void read_line(char string[], int max){
    int c, i = 0;
    while (i < max-1 && (c = getchar()) != '\n' && c != EOF)
        string[i++] = c;
}

int main(void)
{
    printf("Enter a string: ");
    read_line(gs1, MAX);
    expand(gs1, gs2);
    printf("\nThe expanded string: %s.\n", gs2);
    return 0;
}