2. Spotting repeating code

Let's start with a fairly simple program:

 
                 SET FirstNumber TO 37
                 IF FirstNumber > 100 THEN
	                  SET FirstNumber TO 100
	                  SET SecondNumber TO FirstNumber * 0.15
	                  SEND SecondNumber TO DISPLAY
                 END IF 
				 
			

Now imagine a program that wants to carry out the same steps, but for a bunch of different numbers. It might look like this:

 
                 SET FirstNumber TO 137
                 IF FirstNumber > 100 THEN
	                  SET FirstNumber TO 100
	                  SET SecondNumber TO FirstNumber * 0.15
	                  SEND SecondNumber TO DISPLAY
                 END IF 
				 

 
                 SET FirstNumber TO 540
                 IF FirstNumber > 100 THEN
	                  SET FirstNumber TO 100
	                  SET SecondNumber TO FirstNumber * 0.15
	                  SEND SecondNumber TO DISPLAY
                 END IF 
				 

 
                 SET FirstNumber TO 320
                 IF FirstNumber > 100 THEN
	                  SET FirstNumber TO 100
	                  SET SecondNumber TO FirstNumber * 0.15
	                  SEND SecondNumber TO DISPLAY
                 END IF 
				 

This will work, but it looks a little clunky. The same lines of code are repeated over and over again. This is inefficient and it also makes it more likely that a programmer will introduce a mistake into the code.

It would be much more efficient to give that batch of steps a label, and then just use that label to refer to it whenever necessary.

This is what subprograms are for.