/**
 * An example of the use of qsort to sort an array of chars
 * Also, a qsort inspired array printing function.
 * 
 * @author gtowell
 * Created: April 2021
 * **/

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

#ifndef NULL
#define NULL (void *)0
#endif

/**
 * A comparison function for passing into qsort
 * This comparison function requires that that array
 * being sorted just contains characters
 * @param p -- a pointer to a location in the array
 * @param q -- a pointer to another location in the array
 * @return an int describing the relation between p and q
 * less than 0 if p<q, greater than 0 is p>q, equal 0 is p==q
 * **/
int compareChar(const void * p, const void * q) {
    const char *pc = p;
    const char *qc = q;
    return *pc - *qc;
}

/**
 * A ridiculously complex way to print an array, but reasonably
 * generic and, even better, it follows qsort
 * @param base -- a pointer to the start of the array -- or at
 * least the start of the portion of the array to be printed
 * @param nmemb -- the number of item in the array (or at least 
 * the number of items to be printed)
 * @param size -- the number of bytes of the items in the array
 * @param fmt -- a formatting string 
 * **/
void parray2(void * base, size_t nmemb, size_t size, char* fmt) {
    for (int i = 0; i < nmemb; i++) {
        char c = *((char *)base);
        printf(fmt, c);
        base += size;
    }
    printf("\n");
}

/**
 * Fill an array with random chars, print it, sort it, 
 * print it again
 * **/
int main(int argc, char const *argv[]) {
    srand(time(NULL));
    char aa[100];
    // fill the array with random chars
    for (int i = 0; i < 100; i++)
        aa[i] = 'a' + (rand() % 26);
    parray2(aa, 100, sizeof(char), "%c");
    qsort(aa, 100, sizeof(char), compareChar);
    parray2(aa, 100, sizeof(char), "%c");
    return 0;
}