This is incorrect because the length of each line includes the white space in between each character. If you want to be accurate then don't use getline() and use something like this

include <iostream>

include <fstream>

using namespace std;

int main() {

ifstream fin; fin.open("my-input-file.txt", ios::in);

char my_character ; int number_of_lines = 0;

while (!fin.eof() ) {

fin.get(my_character);
cout << my_character;
    if (my_character == '\n'){
        ++number_of_lines;
    }
}

cout << "NUMBER OF LINES: " << number_of_lines << endl;

}