frequency.c

#include <stdio.h>

#define ALPHABET 26

int main (void) {

    int lettersUpper[ALPHABET] = {0};
    int lettersLower[ALPHABET] = {0};

    int c = getchar();
    while (c != -1) {
        if (c >= 'A' && c <= 'Z') {
            lettersUpper[c-'A']++;
        } else if (c >= 'a' && c < 'z') {
            lettersLower[c-'a']++;
        }
        c = getchar();
    }

    for (int i = 0; i < ALPHABET; i++) {
        printf ("%c: %d\t%c: %d\n", 'a'+i, lettersLower[i], 'A'+i, lettersUpper[i]);
    }

    return 0;
}