Example: Sorting Names using qsort in C

// Sorting Names using qsort
#include <stdio.h>
#include <string.h> // Required for strcmp
#include <stdlib.h> // Required for qsort

#define MAX_NAMES 5

// Comparison function required by qsort
// It takes two const void pointers, which qsort will cast to the type of array elements
int compareStrings(const void *a, const void *b) {
    // Step 1: Cast the void pointers to char**
    // This allows us to dereference them to get the actual char* (string)
    const char **str_a = (const char **)a;
    const char **str_b = (const char **)b;
    
    // Step 2: Use strcmp to compare the actual strings
    return strcmp(*str_a, *str_b);
}

int main() {
    // Step 3: Initialize an array of string pointers
    char *names[MAX_NAMES] = {
        "Charlie",
        "Alice",
        "Bob",
        "David",
        "Eve"
    };
    int i;

    // Step 4: Print the original list of names
    printf("Original names:\n");
    for (i = 0; i < MAX_NAMES; i++) {
        printf("%s\n", names[i]);
    }
    printf("\n");

    // Step 5: Call qsort
    // Parameters:
    // 1. base: Pointer to the first element of the array to be sorted.
    // 2. num: Number of elements in the array.
    // 3. size: Size in bytes of each element in the array.
    // 4. compar: Pointer to a comparison function.
    qsort(names, MAX_NAMES, sizeof(char *), compareStrings);

    // Step 6: Print the sorted list of names
    printf("Sorted names (qsort):\n");
    for (i = 0; i < MAX_NAMES; i++) {
        printf("%s\n", names[i]);
    }

    return 0;
}