trying to write a letter counter in C - c

Question

I am trying to make a program that counts the number of letters that the user has input. When I run my program, it says error: expected ';' after expression on the line count_letters(){ // writing the function to count number of letters? Does a function need a semicolon at the end? I also feel that I am not approaching this problem correctly, can someone please enlighten me :(
#include <stdio.h>
#include <cs50.h>
#include <string.h>
#include <ctype.h>
int count_letters(); //function to count letters
int number_of_letters; //length of the string input
int letterCount; // counter for number of letters in the string input
int main(void) {
string text = get_string("Text: "); // getting string input
number_of_letters = strlen(text); //storing the length of string here
printf("Number of letters: %i\n", letterCount); //printing the number of letters in the string input
count_letters() { // writing the function to count number of letters
for (int i = 0; i < number_of_letters; i++) {
if (isalpha(text[i])) {
letterCount++;
}
}
}
}

Answer 1

While you are free to use strlen to get the initial number of characters in text, it isn't necessary. In C, the last character in a "string" is the nul-terminating character '\0' (which has the ASCII value of 0). This is what differentiates a normal array of characters, from a string. It is how all string functions know when to stop scanning for characters.
So you don't need to know beforehand how many characters there are in a string. For example, take the string "hello" entered at the "Text: " prompt where you have declared.
string text = get_string("Text: ");
When you enter "hello" at the prompt:
Text: hello
The string is stored in memory as:
+---+---+---+---+---+---+
| h | e | l | l | o |\0 |
+---+---+---+---+---+---+
^
|
text
where the pointer text points to the address of the first character of the string in memory. Using the fact that a string ends with a nul-terminating character, you can simply scan forward from the start until your reach '\0' (equivalent to plain old 0).
You can use a for loop and iterate using indexes:
for (int i = 0; text[i]; i++)
// do whatever with the character text[i]
Or you can use a pointer and simply increment the pointer so it points to the next character in the string until the '\0' is reached:
string p = text;
while (*p) {
// do whatever with *p (the character at that address)
p++;
}
Putting the last version into your int count_letters (string s) function (that passes a pointer to your string as a parameter to the function) and returns an int representing the number of letters (including only [a-zA-Z]), your function reduces to:
int count_letters (string s)
{
int n = 0;
while (*s) /* while not the nul-character */
if (isalpha (*s++)) /* check if current is letter, advance ptr */
n++; /* increment letter count */
return n; /* return letter count */
}
You main() function, not needing to call strlen() then reduces to:
int main (void) {
string text = get_string ("Text: ");
printf ("Number of letters: %d\n", count_letters(text));
}
Putting it altogether and including the needed headers, you would have:
#include <stdio.h>
#include <ctype.h>
#include "cs50.h"
int count_letters (string s)
{
int n = 0;
while (*s) /* while not the nul-character */
if (isalpha (*s++)) /* check if current is letter, advance ptr */
n++; /* increment letter count */
return n; /* return letter count */
}
int main (void) {
string text = get_string ("Text: ");
printf ("Number of letters: %d\n", count_letters(text));
}
Example Use/Output
Compile and link with the libcs50.so and then, for example you would have:
$ ./bin/ltrcountcs50
Text: hello world
Number of letters: 10
Understanding what a "string" in C is (outside of the unfortunate choice of the typedef char* string; used by CS50), allows you to handle scanning over the characters in your string without needing to know how many characters are included beforehand. (and also helps you understand why failing to provide a nul-terminated string to any of the C string function that expect a nul-terminated string as a parameter results in Undefined Behavior -- they have no way of knowing when to stop scanning for characters).
Look things over and let me know if you have further questions.

Answer 2

#include <stdio.h>
#include <cs50.h>
#include <string.h>
#include <ctype.h>
int count_letters(); //function to count letters
int number_of_letters; //length of the string input
//initialize letterCount to 0 so that doing letterCount++ does not add 1 to a garbage value
int letterCount = 0; // counter for number of letters in the string input
//define string as a global value if you don't want to refer to it again and again by pass it as parameter or reference
string text;
void count_letters() { //since it's not returning anything, it's void not integer
for(int i = 0; i < number_of_letters; i++) {
if(isalpha(text[i])
letterCount++;
}
}
int main(void){
text = get_string("Text: "); // getting string input
number_of_letters = strlen(text); //storing the length of string here
printf("Number of letters: %i\n", letterCount); //printing the number of letters in the string input
}
Hope this helps. All the comments are there where any modifications are made

Answer 3

I might take your knowledge for being too basic, please forgive me if it is the case.
I believe you have made a small mistake possibly led by the way another language works. The problem lies in the way you have declared count_letters().
To properly declare a function in C, first get out of any existing function, then enter any variable type as a return type for your function, the name of your function, then, in parenthesis, your function's parameters. And after that, your function's code can be inserted between brackets, like you did.
Note you can also declare the function without the code, then put the code for the function lower.
And you might also want to declare your string externally to avoid dealing with pointers.
Here's an example of function declaration:
int foo(int amount)
Hence your code should look a little like this:
#include <stdio.h>
#include <cs50.h>
#include <string.h>
#include <ctype.h>
void count_letters(); //function to count letters
int number_of_letters; //length of the string input
int letterCount; // counter for number of letters in the string input
string text;
int main(void) {
text = get_string("Text: "); // getting string input
number_of_letters = strlen(text); //storing the length of string here
count_letters();
printf("Number of letters: %i\n", letterCount); //printing the number of letters in the string input
}
void count_letters() { // writing the function to count number of letters
for (int i = 0; i < number_of_letters; i++) {
if (isalpha(text[i])) {
letterCount++;
}
}
}
Now please excuse me if I did not understand or answer your question correctly, it would be with pleasure I'd improve myself if I could get more detail. Lacking the cs50.h library, I cannot know for sure my code works.

Answer 4

#include <stdio.h>
#include <cs50.h>
#include <string.h>
#include <ctype.h>
int count_letters(char *); //function to count letters
int main(void)
{
char* text = get_string("Text: "); // getting string input
printf("Number of letters: %i\n", count_letters(text)); //printing the number of letters in the string input
}
int count_letters(char *text)
{ // writing the function to count number of letters
int letterCount,number_of_letters; //length of the string input
number_of_letters = strlen(text); //storing the length of string here
for(int i = 0; i < number_of_letters; i++){
if(isalpha(text[i]))
{
letterCount++;
}
return letterCount;
}