Getting unexpected results in CS50 readability problem - c

Question

In solving this readability problem, I have been getting some weird unexpected results(expected Grade 16+, getting Grade 10 etc etc), I am not being able to figure out where the bug is or how can I solve it, please help me figure out the bug. The codes are as follows:
//includes
#include <stdio.h>
#include <cs50.h>
#include <string.h>
#include <math.h>
//global variables
int lc; //letter count
int wc; //word count
int sc; //sentence count
bool awc; //already word counted
double L; //average number of letters per 100 words
double S; //average number of sentences per 100 words
float index;
//function declaration
int count_letters(string x);
int count_words(string x);
int count_sentences(string x);
//main
int main(void)
{
string text = get_string("text : ");
count_letters(text);
printf("%i letters\n", lc);
count_words(text);
printf("%i words\n", wc);
count_sentences(text);
printf("%i sentences\n", sc);
L = lc / wc * 100.0f;
S = sc / wc * 100.0f;
index = (0.0588 * L) - (0.296 * S) - 15.8;
if(index < 1)
{
printf("Before Grade 1\n");
}
else if(index >= 16)
{
printf("Grade 16+\n");
}
else
{
printf("Grade %i\n", (int) round(index));
}
}
//functions
int count_letters(string x)
{
lc = 0;
for(int i = 0, n = strlen(x); i < n; i++)
{
if((x[i] >= 'a' && x[i] <= 'z') || (x[i] >= 'A' && x[i] <= 'Z'))
{
lc += 1;
}
}
return lc;
}
int count_words(string x)
{
wc = 0;
awc = false;
for(int i = 0, n = strlen(x); i < n; i++)
{
if((x[i] >= 'a' && x[i] <= 'z') || (x[i] >= 'A' && x[i] <= 'Z'))
{
if(awc == false)
{
wc += 1;
awc = true;
}
}
if(x[i] == ' ')
{
awc = false;
}
}
return wc;
}
int count_sentences(string x)
{
sc = 0;
for(int i = 0, n = strlen(x); i < n; i++)
{
if(x[i] == '.' || x[i] == '!' || x[i] == '?')
{
sc += 1;
}
}
return sc;
}
The number of letters, words and sentences from these functions are correct so far so I think the problem lies in the main section, probably something to do with the variable type of "L" and "S" or the index formulae, please help me figure out where the problem is. Thank you
here are some of the tests: sentences(expected results)
1.One fish. Two fish. Red fish. Blue fish. (Before Grade 1)
2.Harry Potter was a highly unusual boy in many ways. For one thing, he hated the summer holidays more than any other time of year. For another, he really wanted to do his homework, but was forced to do it in secret, in the dead of the night. And he also happened to be a wizard. (Grade 5)
3.A large class of computational problems involve the determination of properties of graphs, digraphs, integers, arrays of integers, finite families of finite sets, boolean formulas and elements of other countable domains. (Grade 16+)

Answer 1

L = lc / wc * 100.0f;
wrong
L = 100.0f * lc / wc;
right.
When both operands of / are integers, the result is integer as well, so 5/3 == 1.

Answer 2

the OPs code contains several problems, as discussed in the comments to the question.
The following proposed code:
corrects those problems exposed in the comments
cleanly compiles
strongly suggest all those 'global' variables be moved to inside the appropriate functions and when needed else where be passed as parameters.
and now, the proposed code:
//includes
#include <stdio.h>
#include <cs50.h>
#include <string.h>
#include <math.h>
//global variables
int lc; //letter count
int wc; //word count
int sc; //sentence count
bool awc; //already word counted
double L; //average number of letters per 100 words
double S; //average number of sentences per 100 words
double i;
//function declaration
int count_letters(string x);
int count_words(string x);
int count_sentences(string x);
//main
int main(void)
{
string text = get_string("text : ");
count_letters(text);
printf("%i letters\n", lc);
count_words(text);
printf("%i words\n", wc);
count_sentences(text);
printf("%i sentences\n", sc);
L = lc / wc * 100.0;
S = sc / wc * 100.0;
i = (0.0588 * L) - (0.296 * S) - 15.8;
if(i < 1.0)
{
printf("Before Grade 1\n");
}
else if(i >= 16.0)
{
printf("Grade 16+\n");
}
else
{
printf("Grade %i\n", (int) round(i));
}
}
//functions
int count_letters(string x)
{
lc = 0;
for( size_t i = 0, n = strlen(x); i < n; i++)
{
if((x[i] >= 'a' && x[i] <= 'z') || (x[i] >= 'A' && x[i] <= 'Z'))
{
lc += 1;
}
}
return lc;
}
int count_words(string x)
{
wc = 0;
awc = false;
for( size_t i = 0, n = strlen(x); i < n; i++)
{
if((x[i] >= 'a' && x[i] <= 'z') || (x[i] >= 'A' && x[i] <= 'Z'))
{
if(awc == false)
{
wc += 1;
awc = true;
}
}
if(x[i] == ' ')
{
awc = false;
}
}
return wc;
}
int count_sentences(string x)
{
sc = 0;
for( size_t i = 0, n = strlen(x); i < n; i++ )
{
if(x[i] == '.' || x[i] == '!' || x[i] == '?')
{
sc += 1;
}
}
return sc;
}