OK, got a new Mac (independently from the system operating on it). here are a few things to be done to get going and develop code;

Install Homebrew

Home-brew (or brew, very shortly) is a very useful utility which allows one to install packages which aren't on a new computer and which did not come with the operating system. Ideally, this is the first package one should install.

/bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install.sh)"

at this point, new formulas can be installed with:

brew install package_name

updated with:

brew update package_name

and removed with:

brew uninstall package_name

to list all installed formulae, use:

brew list or brew list --full-name

Install compilers (clang in particular)

For MacOS<10.10, compilers (and command line tools in general) used to be strongly coupled to Xcode. With more recent versions of MacOS, command line tools can be installed independently from Xcode (which is a major advantage, as Xcode is a very big and heavy beast.

Command line tools from brew

Recent versions of Homebrew install the Xcode command line tools by default. After the brew installation, try g++ -v to see if a c++ was already installed for you.

Installing command line tools

Open a terminal and type:

xcode-select --install

That should be it!

Installing Xcode

Go to the App Store, search for Xcode and install it. Did I not say it is huge? Command line tools have to be installed manually, anyway...