Error invalid operands to binary expression - c

Question

I've been working on readability and I really am stuck as to what I've done wrong/what I'm missing.
#include <stdio.h>
#include <math.h>
#include <cs50.h>
#include <string.h>
#include <ctype.h>
int main() {
string text = get_string("Text: ");
int sentences = 0;
int numberOfCharacters = strlen(text);
string characters[numberOfCharacters];
int words = 0;
for (int i = 0; i == numberOfCharacters; i++) {
if (isspace(characters[i]) == 0) {
words ++;
}
}
for (int i=0; i < numberOfCharacters; i++) {
if (text[i]=='.') {
numberOfCharacters++;
}
}
int averageWords = characters / words * 100;
int index = 0.0588 * round(characters) - 0.296 * round(sentences) - 15.8;
printf("Grade %d \n", index);
}
The error I get from that, using help50, is: readability.c:26:35: error: invalid operands to binary expression ('string [numberOfCharacters]' and 'int')
Which I don't understand, so please if possible help :)

Answer 1

In cs50 string is a typedef of char*, so what you have there is:
char *characters[numberOfCharacters];
Which is an array of pointers, they are not initialized in any way, in your next statements you accessing these unitialized values and you are passing an incompatible argument to isspace.
Furthermore, the expression:
int averageWords = characters / words * 100;
Is odd, you're dividing an array of pointers to char (wich decays to a pointer, but that's beside the point), by an int. That's where the error stems from, but you need to correct the rest.
Not to mention round(characters) which is also very strange, that function expects a double argument, but again, you are passing to it an array of pointers.

Answer 2

The name string is defined as an alias for the type char *. So this declaration
string characters[numberOfCharacters];
is equivalent to the declaration
char * characters[numberOfCharacters];
So in this expression
isspace(characters[i]) == 0
the argument characters[i] has the type char * while the function expects an argument of the type int.
So you need at least to declare
char characters[numberOfCharacters];
But in any case this loop
for (int i = 0; i == numberOfCharacters; i++) {
if (isspace(characters[i]) == 0) {
words ++;
}
}
does not make a sense because the array characters was not initialized.
It seems within this loop you were going to use text instead of characters.
This expression
int averageWords = characters / words * 100;
is entirely wrong and does not make a sense. You are trying to divide a pointer ( after implicit conversion the array characters to a pointer to its first element) by an integer. But such an operation is not defined for pointers.
So it is unclear what the program does.

Answer 3

First Issue:
string is defined as char * so this is wrong:
string characters[numberOfCharacters];
That is giving you an array of strings, not a string of length numberOfCharacters
Change that to this:
char characters[numberOfCharacters];
Second Issue:
characters is uninitialized when first used, you could of meant to use text instead in the loop
Third Issue:
Performing math (round(characters) and characters / words * 100) on a string or array is certainly wrong and makes no sense, so I am not sure what you are attempting to do here
I reviewed the clear issues, but since it is unclear what your program is trying to do, I cannot provide further feedback