The boolean type is chosen to indicate true or false. The initial value for y should be either true or false, not 1.
What do you have connected to analog pins 0 to 3?
Your line follower currently reads the values coming from 4 sensors, every 20 milliseconds, for 10 seconds, and keeps the largest and smallest value from each pin.
After 10 seconds, it prints the largest and smallest values from each pin.
After that, it does nothing. Hard to follow the line that way, but it IS good that you are developing in stages.
What changed between being able to upload, and not being able to?