QUESTION 2:
Can you think of some machines which DON'T have cycles in them?
CONTROL-BREAK does indeed end the program, and that is the problem. What if you wanted the program to do more than one loop? What if you wanted to do one loop followed by another loop? We need a way to end the first loop without ending the program.
The previous chapter started by discussing how important cycles were to machines. By using cycles, a machine can keep on running for a long time by repeating useful motions. One example of this is an automobile engine.
But how many different repeating motions are there in an engine? Actually, quite a few. The main cycle is the rotation of the crank shaft, but connected to that cycle are the cycles of the individual pistons, the cycles of the water pump, the alternator, the valves, and so on. All these cycles have to be kept "in sync" for the engine to work properly.
Another example of a machine with many cycles is a mechanical clock. Each gear, balance wheel, and spring has its own cycle. And like the engine, they all must synchronize precisely for the machine to work.
Programs, like mechanical machines, can be made of
many different cycles.
This chapter discusses additions to the DO...LOOP
statements that enable this.
Can you think of some machines which DON'T have cycles in them?