How to compile a C++ program on Mac OSX

File "HelloWorld.cpp" contents between the dashed lines:

-----

#include <iostream>

using namespace std;

int main()

{

    cout << "Hello world!" << endl;

    cout << "Hello again!" << endl;

    return 0;

}

-----

Now compile the program:

g++ HelloWorld.cpp -o HelloWorld

Now run the program:

./HelloWorld