How to create a filereading program that loads a file of codes - c++

Question

Basically my program is giving me a load of errors with my filereading program when trying to compile. The goal is to get the user to enter the threshold number and the strings that are equal to or greater than that threshold number will be outputted. The program fails at that because there are several errors with the code. How to fix the errors within the code?
#include <iostream>
#include <fstream>
#include <cstdlib>
using namespace std;
int read_airports(string cities[], int threshold);
int main()
{
ifstream fin;
fin.open("airports.txt");
if (fin.is_open())
{
string cities[20];
int count, threshold;
count = read_airports(cities, threshold);
while(!fin.eof())
{
fin >> threshold;
cout << "Enter a threshold number" << endl;
cin >> threshold;
if (fin.good())
{
if (cities >= threshold)
{
cout << cities << endl;
}
}
}
fin.close();
}
return 0;
}
int read_airports(string cities[], int threshold)
{
}
Here is the text file where this code is based off of.
LAX Los-Angeles 40
JFK New-York 39
IAH Houston 26
LCY London 34
PAR Paris 15
TYO Tokyo 11
SEL Seoul 5
YYZ Toronto 28

Answer 1

[Warning: none of this code has been tested at all.]
I would structure the code rather differently.
I would create a structure for the data about each airport/city:
struct airport {
std::string abbreviation;
std::string city_name;
int threshold;
};
Then I'd overload operator>> to read one of those records from a stream, and operator<< to write one to a stream:
std::istream &operator>>(std::istream &is, airport &ap) {
return is >> ap.abbreviation >> ap.city_name >> ap.threshold;
}
std::ostream &operator<<(std::ostream &os, airport const &ap) {
return os << ap.abbreviation << "\t" << ap.city_name << "\t" << ap.threshold;
}
Then I'd write code to desired data from a file of those to standard output:
std::ifstream infile("airportdata.txt");
std::cout << "Please enter minimum threshold value: ";
int threshold;
std::cin >> threshold;
std::copy_if(std::istream_iterator<airport>(infile), {},
std::ostream_iterator<airport>(std::cout, "\n"),
[=](airport const &ap) { return ap.threshold > threshold; });