Program that calculates flight distance

Question

I am having trouble with a program that uses void functions. I have never used them before so I'm a bit lost. My program has a 3 sets of cities. It is supposed to get the three cities in one of the sets and figure out how long the flight is. My problem is that I keep getting the error that my variables are undefined. This is the first program I have tried using void functions. I have tried initializing every variable by itself but I don't think that is the correct way to do it or is it? Any help would be appreciated. Here is my code:

#include <fstream>
#include <iostream>
#include <string>

using namespace std;
void readFile (int wall1, double &lat1, double &lon1, string &city1,
                       double &lat2, double &lon2, string &city2,
                       double &lat3, double &lon3, string &city3);
void intro();
void askDataSet(int &w);

//--------------------------------------------------
int main()
{

    intro();
    askDataSet(int &w);
    string name;


    int lat1, lat2, lat3, , lon1, lon2, lon3, beginLat, beginLon, beginCity, midLat,  midLon, midCity, endLat, endLon, endCity;
    string city1, city2, city3;
    readFile (beginLat, beginLon, beginCity, midLat, midLon, midCity, endLat, endLon, endCity);
    cout << "The First City at coordinates " << beginLat << " and " << lon1 << " is:  " << city1 << endl;
    cout << "The Second City is at coordinates " << beginLat << " is " << lon2 << ":  " << city2 << endl;
    cout << "The Third City is at coordinates " <<  beginLat << " is " << lon3 << ":  " << city3 << endl;

    leg1 = dist( beginLat, beginLon, midLat, midLon);
    leg2 = dist( midLat, midLon, endLat, endLon);
    nonstop = dist( leg1-leg2 );

    cout << "It is " << dist << "fewer miles for non-stop" << endl;


   system("pause");
   return 0;
 }

 void readFile (int &wall1, double &lat1, double &lon1, string &city1,
                 double &lat2, double &lon2, string &city2,
                 double &lat3, double &lon3, string &city3)
{
   ifstream dataIn;
   dataIn.open("cities.txt");
   if(dataIn.fail())
{
    cout << "Error.  File does not exist. " << endl;
    exit(1);
}

    dataIn >> lat1;
    dataIn >> lon1;
    dataIn.get();
    getline(dataIn, city1);
    dataIn >> lat2;
    dataIn >> lon2;
    dataIn.get();
    getline(dataIn, city2);
    dataIn >> lat3;
    dataIn >> lon3;
    dataIn.get();
    getline(dataIn, city3);

}

    void intro()
    {
    cout << "In this lab we will try to figure out how much shorter it is to fly non-stop compared to one-stop." << endl;
    cout << endl;
    }

    void askDataSet(int &w)
    {
     cout << "Which set of cities would you like to figure the distances for? " << endl; 
     cin >> w;
    }

Answer 1

To give back a value from a void function via a reference-parameter, a variable has to exist in the caller's scope which is given as the parameter.

So in your case, for example to call askDataSet , you first have to declare an int to hold the result:

int w;
askDataSet(w);

Then askDataSet will write into your integer variable and you can use it after the call.

Further points I noticed with the code:

• For the readFile call, the variables passed must have the same type as the parameters ( double , not int ).
• There is an extra comma in the declarations before the readData call: " lat3, , lon1 "
• Maybe you'll want to replace beginLat , midLon etc. with lat1 , lon2 (or the other way around).
• readFile seems to have an unused first argument int wall1 , which is missing in the readFile -call in main .
• The dist function is not defined and at the end of main you try to print it.
• To use system and exit , you should #include <cstdlib> .