Make a controller for a car. Have subroutines that, speed the car up by 1mph if below a set speed (eg 60mph), slow the car down by 1mph if above a set speed (eg 70mph), do nothing if in an acceptable band (eg 60-70mph). Start the car at a speed, use an infinite while loop to control the car (ctrl C to exit). Add a rocket that boosts the car's speed at random times, and by a random amount if in the steady speed band.

Change the routines to loop until they reach the required speed and then return

Change the routines to recursively call themselves till they reach the required speed and then return.