usaco-guide/content/1_Intro/Running_Cpp.md

id	title	author	description
running-cpp	Running C++	Nathan Wang, Benjamin Qi, Anthony Wang	Running C++ both online and locally.

Running C++ Online

• OnlineGDB
  • online compiler with an embedded GDB debugger
  • can be buggy sometimes
  • supports files and file I/O
• CSAcademy
  • pretty nice (unless you get "Estimated Queue Time: ...")
  • "saved locally" will not save your code if you close the tab, press Command-S to save.
• Ideone
  • okay ... with an ad blocker
  • make sure your code is not public
  • sometimes erases your code when you first create it (so get in the habit of copying your code first)

You can't use file I/O on the latter two websites. You can also share code with pastebin or hastebin.

Running C++ Locally

On Mac

Clang is the default compiler for Mac OS X, but you should use GCC's g++ since that's what USACO uses to compile your code.

Installation

First, open Terminal and familiarize yourself with some basic commands.

• Intro to OS X Command Line.
• Mac Terminal Cheat Sheet

You will also need to install Homebrew.

Run

brew install gcc

According to this if brew doesn't seem to finish for a long time then

brew install gcc --force-bottle

probably suffices.

Confirmation

You should be able to compile with g++ or maybe g++-#, where # is the version number (currently 9). Running the following command:

g++-9 --version

should display something like this:

g++-9 (Homebrew GCC 9.2.0_2) 9.2.0
Copyright (C) 2019 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

Troubleshooting

Make sure you have installed XCode command line tools.

xcode-select --install # make sure x-code command line tools are installed
softwareupdate --list
softwareupdate -i -a # installs everything

On Windows

Like Windows in general, you have a lot of options for running C++.

The easiest option is to use an IDE such as Codeblocks or Visual Studio because they often have C++ support already built-in. See the IDEs section below for more information.

However, you can also use MinGW if you prefer compiling and running C++ using the command line. Another good option is Windows Subsystem for Linux (WSL) which is what I personally use, although it may be more difficult to properly set up.

Installing MinGW

First, download and run the MinGW installer. Once it's installed, open the MinGW Installation Manager, click on Basic Setup on the left, and select mingw32-gcc-g++-bin for installation.

Adding MinGW to PATH

Installing WSL

VSCode Docs (difficult for beginners)

On Linux

GCC is usually preinstalled on most Linux distros. You can check if it is installed with

whereis g++

If it is not preinstalled, you can probably install it using your distro's package manager.

Running With the Command Line

Consider a simple program such as the following, which we'll save in name.cpp.

#include <bits/stdc++.h>
using namespace std;

int main() {
  int x; cin >> x;
  cout << "FOUND " << x << "\n";
}

It's not hard to compile & run a C++ program. First, open up Powershell on Windows or Terminal on Mac. We can compile name.cpp into an executable named name with the following command:

g++ name.cpp -o name

Then we can execute the program:

./name

If you type some integer and then press enter, then the program should produce output. We can write both of these commands in a single line:

g++ name.cpp -o name && ./name

Redirecting Input & Output

If you want to read input from inp.txt and write to out.txt, then use the following:

./name < inp.txt > out.txt

See "Intro - Introductory Problems" for how to do file input and output within the program.

Compiler Options (aka Flags)

Use compiler flags to change the way GCC compiles your code. Usually, we use the following in place of g++ name.cpp -o name:

g++ -std=c++17 -O2 name.cpp -o name -Wall -Wextra -Wshadow

Explanation:

• -O2 tells g++ to compile your code to run more quickly (see here)
• -std=c++17 allows you to use features that were added to C++ in 2017. USACO uses -std=c++11.
• -Wall -Wextra -Wshadow checks your program for common errors. See "General - Debugging" for more information about these.
• Summary of Options

You should always compile with these flags.

Adding Shortcuts (Mac and Linux only)

(alternatives for Windows?)

Of course, retyping the flags above can get tedious. You should define shortcuts so you don't need to type them every time!

Aliases in Terminal

Open your bash profile with a text editor such as gedit (or sublime text).

brew install gedit
gedit ~/.zshenv

You can add aliases and functions here, such as the following to compile and run C++.

co() { g++ -std=c++17 -O2 -o $1 $1.cpp -Wall -Wextra -Wshadow; }
run() { co $1 && ./$1 & fg; }

Now you can easily compile and run name.cpp from the command line with co name && ./name or run name. Note that all occurrences of $1 in the function are replaced with name.

Tools

IDEs

• Geany
• Visual Studio Code
  • lightweight, fast IDE, but requires some configuration
• Visual Studio
  • heavier cousin of Visual Studio Code
• XCode
  • Mac only
• Codeblocks
  • bad on Mac
• CLion
  • requires a license, but free for students

Text Editors

Run with the command line.

• Sublime Text 3
  • a fast, lightweight text editor for Windows, Mac, and Linux
  • Editing Build Settings
  • FastOlympicCoding Addon
  • Sublime Snippets
  • Symlink
    • Using /usr/local/bin/subl instead of ~/bin/subl worked for me on OS X Mojave.
• Atom
  • another text editor for Windows, Mac, and Linux from the makers of Github
• Vim
  • classic text editor, usually preinstalled on Mac and Linux, and also available for Windows
  • probably easiest way to print syntax-highlighted code on Mac, see the response to this post
• Others?