Compiling simple Hello World program on OS X via command line

Try

g++ hw.cpp
./a.out

g++ is the C++ compiler frontend to GCC.
gcc is the C compiler frontend to GCC.

Yes, Xcode is definitely an option. It is a GUI IDE that is built on-top of GCC.

Though I prefer a slightly more verbose approach:

#include <iostream>

int main()
{
    std::cout << "Hello world!" << std::endl;
}

g++ hw.cpp -o hw
./hw

user@host> g++ hw.cpp
user@host> ./a.out

Compiling it with gcc requires you to pass a number of command line options. Compile it with g++ instead.

Also, you can use an IDE like CLion (JetBrains) or a text editor like Atom, with the gpp-compiler plugin, works like a charm (F5 to compile & execute).