CS50- Readability prints only "Before Grade 1"

Question

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

int main(void) { string Text = get_string("What is the text? \n");

int letters = 0;
int words = 1;
int sentences = 0;

for (int i = 0, n = strlen(Text); i < strlen(Text); i++)
{
    if (isalpha(Text[i]))
    {
        letters++;
        /*printf("%i", letters);*/
    }
    {
     if (isspace(Text[i]))
    {
        words++;
         printf("%i", words);
    }
    else if (Text[i] == '.' || Text[i] == '!' || Text[i] == '?')
    {
         sentences++;
        printf("%i", sentences);
    }
}
    //use Coleman-Liau Index
    float calculation = (0.0588 * letters / words * 100) - (0.0296 * sentences / words * 100) 
- 15.8;

    int index = round(calculation);

    if (index < 1)
    {
        printf("Before Grade 1\n");
        return 0;
    }
    else if (index >= 16)
    {
        printf("Grade 16+\n");
        return 0;
    }
    else
    {
        printf("Grade %i\n", index);
    }
}

}`

If I remove the return function, it prints out numerous grades which are all different. If I print out with returns included, no matter the Text. it prints out : Before Grade 1. I don't know what I'm doing wrong.