readability.c

#include <cs50.h>
#include <stdio.h>
#include <string.h>
#include <math.h>

int count_letters(string text);
int count_words(string text);
int count_sentences(string text);
int getGradeLevel(int letters, int words, int sentences);

int main(void)
{
    string text = get_string("Text: ");

    int cl = count_letters(text),
        cw = count_words(text),
        cs = count_sentences(text);

    int grade_level = getGradeLevel(cl, cw, cs);

    if (grade_level < 1)
    {
        printf("Before Grade 1\n");
    }
    else if (grade_level >= 16)
    {
        printf("Grade 16+\n");
    }
    else
    {
        printf("Grade %d\n", grade_level);
    }

    return 0;
}

int count_letters(string text)
{
    int count = 0;

    for (int i = 0, n = strlen(text); i < n; i++)
    {
        if (isalpha(text[i]))
        {
            count++;
        }
    }

    return count;
}

int count_words(string text)
{
    int count = 1;

    for (int i = 0, n = strlen(text); i < n; i++)
    {
        if (isspace(text[i]))
        {
            count++;
        }
    }

    return count;
}

int count_sentences(string text)
{
    int count = 0;

    for (int i = 0, n = strlen(text); i < n; i++)
    {
        if (text[i] == '.' || text[i] == '!' || text[i] == '?')
        {
            count++;
        }
    }

    return count;
}

int getGradeLevel(int letters, int words, int sentences)
{
    float L = (float) letters / words * 100;
    float S = (float) sentences / words * 100;

    return round(0.0588 * L - 0.296 * S - 15.8);
}