Warning: require(/var/www/vendor/autoload.php): failed to open stream: code example

Example 1: laravel require vendor autoload

//Try to run either:
	composer install
//or
    composer update

Example 2: failed to open stream: No such file or directory in artisan on line 18

The error is due to missing vendor folder.
You just need to run `composer install` in the project directory which will 
create a folder named vendor which will have all composer libraries and 
`autoload.php` file.