Character Frequency Analysis : Part 3 of a Series

#include <stdio.h>
#include <ctype.h>

typedef struct CHAR_FREQUENCY_ANALYSIS_
{
    size_t Frequency;
    double Percentage;
    unsigned char Character;
}CHAR_FREQ_ANAL;

int printCFA(CHAR_FREQ_ANAL *);

main(int argc, char *argv[])
{
    FILE *data;
    CHAR_FREQ_ANAL cfa[26] = {{0, 0, 0}};
    size_t thisEntry;
    size_t thisByte;
    size_t fileLen;
    char *prog = argv[0];
    unsigned char alphabet[] = "abcdefghijklmnopqrstuvwxyz";
    unsigned char ch;
    size_t count = 0;
    int pos;

    /* file handling */
    if(argc == 1)
    {
        fprintf(stderr, "ERROR: %s requires a target file.\n", prog);
        exit(1);
    }
    else
    {
        if((data = fopen(*++argv, "r")) == NULL)
        {
            fprintf(stderr, "ERROR: %s cannot open file %s\n", prog, *argv);
            exit(1);
        }
    }

    /* find the file length */
    fseek(data, 0L, SEEK_END);
    fileLen = ftell(data);
    fseek(data, 0L, SEEK_SET);

    /* initialize the structure members */
    for(thisEntry = 0; thisEntry < 26; thisEntry++)
    {
        cfa[thisEntry].Frequency = 0;
        cfa[thisEntry].Percentage = 0.0;
        cfa[thisEntry].Character = alphabet[thisEntry];
    }

    /* get a char and if its alphabetic update the struct */
    for(thisByte = 0; thisByte < fileLen; thisByte++)
    {
        if(isalpha(ch = fgetc(data)))
        {
            pos = tolower(ch) - 'a';
            ++cfa[pos].Frequency;
            ++count;
        }
    }
    
    /* run thru the array and calculate the Frequency */
    for(thisEntry = 0; thisEntry < 26; thisEntry++)
    {
        cfa[thisEntry].Percentage = (double) cfa[thisEntry].Frequency * 100.0 / count;
    }

    /* Display the Results */
    fprintf(stdout, "Character Frequency Analyzer by typedeaF @ www.osix.net\n\n");
    printCFA(cfa);

    exit(0);
}

int printCFA(CHAR_FREQ_ANAL *cfa)
{
    size_t x;
    printf("Ch Count %%age Ch Count %%age\n");
    for(x = 0; x < 13; x++)
    {
        printf(" %c %9lu %6.3f %c %9lu %6.3f\n", cfa[x].Character, (unsigned long)cfa[x].Frequency, cfa[x].Percentage, cfa[x + 13].Character, (unsigned long)cfa[x + 13].Frequency, cfa[x + 13].Percentage);
    }
    return 0;
}