histogram

#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#define OFILE_NAME "histo.txt"
#define SIGMA 'z' - 'a' + 1
int freqLow[SIGMA], freqUp[SIGMA], total;

FILE *safeOpenFile(const char *const path, const char *const mode) {
    FILE *file = NULL;
    file = fopen(path, mode);
    if (file == NULL) {
        perror("opening error!");
        exit(EXIT_FAILURE);
    }
    return file;
}

void safeCloseFile(FILE *file) {
    if (fclose(file) == EOF) {
        perror(NULL);
    }
}

void getFreq(const char *const path) {
    FILE *file = safeOpenFile(path, "r");
    for (char ch; (ch = fgetc(file)) != EOF;) {
        if (!isalpha(ch)) {
            continue;
        }
        if (islower(ch)) {
            freqLow[ch - 'a']++;
        } else {
            freqUp[ch - 'A']++;
        }
        total++;
    }
    safeCloseFile(file);
}

void writeHisto(const char *const path) {
    FILE *file = safeOpenFile(path, "w");
    for (char ch = 'a'; ch <= 'z'; ch++) {
        if (!freqLow[ch - 'a']) {
            continue;
        }
        fprintf(file, "%c - %g%%\n", ch, 100.0 * freqLow[ch - 'a'] / total);
    }
    for (char ch = 'A'; ch <= 'Z'; ch++) {
        if (!freqUp[ch - 'A']) {
            continue;
        }
        fprintf(file, "%c - %g%%\n", ch, 100.0 * freqUp[ch - 'A'] / total);
    }
    safeCloseFile(file);
}

int main(int argc, char **argv) {
    if (argc == 1) {
        fprintf(stderr, "ONE MORE ARG NEEDED!\n");
        exit(-1);
    }
    getFreq(argv[1]);
    writeHisto(OFILE_NAME);
    return 0;
}