How to print out the distance from my function? - c++

Question

I'm very new to C++. This is my first assignment, and I'm having trouble printing out (in main()) the final calculated distance d from my function getairdistance(). My program is shown below and I would appreciate any advice!
#include <iostream>
#include <cmath> //for pi
using namespace std;
void getAirDistance(int *ptr, int *ptr1);
int main(){
struct LOC{
char loc_name[50]; //name of a location on earth
double latitude; //latitude of this location
double longitude; //longitude of this location
}; //structure definition
struct LOC location1;
struct LOC location2; //declared two structures
struct LOC *ptr, *ptr1; //declared two pointers
ptr = &location1; //pointer to the first location structure
ptr1 = &location2; //pointer to the second location structure
cout << "Please enter the name of the first location: "; //print statement
cin.getline(location1.loc_name, 50);//use getline to store the first location
cout << "Please enter the latitude (degrees): "; //print statement
cin >> location1.latitude; //use cin to get the first latitude
cout << "Please enter the longitude (degrees): "; //print statement
cin >> location1.longitude; //use cin to get the first longitude
fflush(stdin);
cout << "Please enter the name of the second location: ";
cin.getline(location2.loc_name, 50);
cout << "Please enter the latitude (degrees): ";
cin >> location2.latitude;
cout << "Please enter the longitude (degrees): ";
cin >> location2.longitude; //exact same thing as above
//getAirDistance(location1, location2);
cout << "The air distance between " << location1.loc_name << " and " << location2.loc_name << " is appx. " << " km. "; //final print statement
}
void getAirDistance(int *ptr, int *ptr1){ //function definition
double long1 = *(ptr + 2) * (M_PI/180); //longitude of first location (rad)
double long2 = *(ptr1 + 2) * (M_PI/180); //longitude of second location (rad)
double lat1 = *(ptr + 1) * (M_PI/180); //latitude of first location (rad)
double lat2 = *(ptr1 + 1) * (M_PI/180); //longitude of first location (rad)
double x = (long2 - long1) * cos((lat1 + lat2)/2); //x coordinate difference
double y = lat2 - lat1; //y coordinate difference
int R = 6371; //Radius of the earth
int d = R * sqrt(pow(x, 2) + pow(y, 2)); //distance between the two locations
cout << d;
}

Answer 1

Make your function return the value of d to the caller (ie main()), eg:
int getAirDistance(int *ptr, int *ptr1);
int main(){
...
int d = getAirDistance(...);
cout << ... << d << ...;
return 0;
}
int getAirDistance(int *ptr, int *ptr1){
...
int d = ...;
return d;
}
That being said, your function takes int* pointers as input, but there are no int variables in your main() code that can be passed to the function. Your use of pointer arithmetic suggests that you think +1 and +2 are accessing the 1st and 2nd fields of the LOC struct, but that is not what happens at all. I suspect what you really meant to do is something more like this instead:
#include <iostream>
#include <cmath> //for pi
using namespace std;
struct LOC{
char loc_name[50]; //name of a location on earth
double latitude; //latitude of this location
double longitude; //longitude of this location
}; //structure definition
int getAirDistance(const LOC &loc1, const LOC &loc2);
int main(){
LOC location1;
LOC location2; //declared two structures
cout << "Please enter the name of the first location: "; //print statement
cin.getline(location1.loc_name, 50);//use getline to store the first location
cout << "Please enter the latitude (degrees): "; //print statement
cin >> location1.latitude; //use cin to get the first latitude
cout << "Please enter the longitude (degrees): "; //print statement
cin >> location1.longitude; //use cin to get the first longitude
fflush(stdin);
cout << "Please enter the name of the second location: ";
cin.getline(location2.loc_name, 50);
cout << "Please enter the latitude (degrees): ";
cin >> location2.latitude;
cout << "Please enter the longitude (degrees): ";
cin >> location2.longitude; //exact same thing as above
int d = getAirDistance(location1, location2);
cout << "The air distance between " << location1.loc_name << " and " << location2.loc_name << " is appx. " << d << " km. "; //final print statement
return 0;
}
int getAirDistance(const LOC &loc1, const LOC &loc2){ //function definition
double long1 = loc1.longitude * (M_PI/180); //longitude of first location (rad)
double long2 = loc2.longitude * (M_PI/180); //longitude of second location (rad)
double lat1 = loc1.latitude * (M_PI/180); //latitude of first location (rad)
double lat2 = loc2.latitude * (M_PI/180); //latitude of second location (rad)
double x = (long2 - long1) * cos((lat1 + lat2)/2); //x coordinate difference
double y = lat2 - lat1; //y coordinate difference
int R = 6371; //Radius of the earth
int d = R * sqrt(pow(x, 2) + pow(y, 2)); //distance between the two locations
return d;
}