This error resulted from using the Composer version supplied by Ubuntu 16.04 with PHP version 7.3

This error came up today when I tried to install TYPO3 with Composer. 

  [ErrorException]                                                                         
  "continue" targeting switch is equivalent to "break". Did you mean to use "continue 2"?

The specific setup being used to create this error was an Ubuntu 16.04 system running PHP 7.3. Many people have encountered this error.

The proposed solution is to remove the Ubuntu supplied version of composer with the following command:

sudo apt-get remove composer

Or if you want to remove everything including configuration files and dependent packages, run:

sudo apt-get purge --auto-remove composer

Then you should install the most recent version of Composer that is available from https://getcomposer.org

There are guides out there on how to do this. Here are some of them in no particular order: