Include and run function from other file - c++

Question

I have 2 files, main.cpp and xyz.cpp, xyz.cppp have function that making some calculation (and should to output it at the end), and i want call this function from switch in main.cpp
main.cpp :
#include <iostream>
#include <math.h>
#include <cstdlib>
#include "xyz.cpp"
int cl;
using namespace std;
int main(int argc, const char * argv[]){
cout << ("Make ur choice (1-1)");
cin >> cl;
switch(cl){
case (1):{
// I suppose it should be called here somehow
}
}
return 0;
}
xyz.cpp:
using namespace std;
int function() {
cout << "Input number: ";
cin >> a;
o1p1 = (1+cos(4*a));
o1p2 = (1+cos(2*a));
o1 = ((sin(4*a))/o1p1)*((cos(2*a))/o1p2);
cout << "\nZ1 = ";
cout << o1;
cout << "\n ";
return 0;
}

Answer 1

Where you have your comment, simply write:
function();
However, note that typically you will want to include header files (i.e. a file with function declarations), rather than source files (a file with the definitions).
In the header you will have:
int function();
The source file would be the same.
Note that this will mean that you will have to compile both source files, rather than just the main one.

Answer 2

Rename your method, otherwise the call is going to be ambiguous.
Use a header file named "xyz.h", where you declare your method. Then, in the main.cpp file, include that header file (instead of its source file). The source file "xyz.cpp" should include the header file as well. Then in main.cpp, just call the method like this: int returnedValue = myFunction();
Complete example:
xyz.h
#ifndef XYZ_H
#define XYZ_H
int myFunction();
#endif /* XYZ_H */
xyz.cpp
#include <iostream>
#include <cmath>
#include "xyz.h"
using namespace std;
int myFunction() {
float a, o1p1, o1p2, o1;
cout << "Input number: ";
cin >> a;
o1p1 = (1+cos(4*a));
o1p2 = (1+cos(2*a));
o1 = ((sin(4*a))/o1p1)*((cos(2*a))/o1p2);
cout << "\nZ1 = ";
cout << o1;
cout << "\n ";
return 0;
}
main.cpp
#include <iostream>
#include "xyz.h"
using namespace std;
int main(int argc, const char * argv[]) {
int cl;
cout << ("Make ur choice (1-1)");
cin >> cl;
switch(cl){
case (1):{
int returnedValue = myFunction();
cout << returnedValue << endl;
}
}
return 0;
}
Output:
Georgioss-MBP:Desktop gsamaras$ g++ main.cpp xyz.cpp -lm
Georgioss-MBP:Desktop gsamaras$ ./a.out
Make ur choice (1-1)1
Input number: 2
Z1 = -2.18504
0