in php you can execute a command via system()
function :
system('YOUR COMMAND - FOR EXAMPLE ./HelloWorld (in your path)');
to get the result you can put it into an variable.
$test=system("some command");
var_dump($test);
In your case:
system('PATH/HelloWorld j'); // runs your HelloWorld executable file
Another solution is using shell_exec()
function. As php.net example:
$output = shell_exec('ls -lart');
echo "<pre>$output</pre>";
each one has its own advantages and disadvantages. You can read more about mentioned functions in php.net/following links:
shell_exec — Execute command via shell and return the complete output as a string