main.c

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

struct leaf_node {
    char ch;
    int frq;
};

int main(int argc, char* argv[]) {

    char ch;
    int ascii_code;
    int arr_ascii_char_frq[256] = {0};

    FILE *fptr = fopen(argv[1], "r");

    // Count char frequencies
    while((ch = fgetc(fptr)) != EOF) {
        ascii_code = (int) ch;
        arr_ascii_char_frq[ascii_code] = arr_ascii_char_frq[ascii_code] + 1;
    }

    // Count frequencies greater than 0
    int count = 0;
    for (int i = 0; i < 256; i++) {
        if (arr_ascii_char_frq[i] > 0) {
            count++;
        }
    }

    // Get subset character frequencies
    char arr_char[count];
    int arr_char_frq[count];
    int j = 0;

    for (int i = 0; i < 256; i++) {
        if (arr_ascii_char_frq[i] > 0) {
            arr_char[j] = (char) i;
            arr_char_frq[j] = arr_ascii_char_frq[i];
            j++;
        }
    }

    for (int i = 0; i < count; i++) {
        printf("%c: %d\n", arr_char[i], arr_char_frq[i]);
    }

    return 0;
}