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subroutines.rst

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basic

Subroutines

Imagine you have a "special piece of code" that's 10 lines long. And you have to use it 7 times in your program. Now, it's not too hard to copy and paste but one can imagine that having to paste 70 lines of the same code can be repetitive and ultimately "ugly". Ugly in the sense that you shouldn't have to repeat yourself.

There is a rule in programming that goes: DON'T REPEAT YOURSELF (DRY)

With subroutines, you can use the same piece of code without copy and pasting.

The structure of a subroutine is as follows: :: YourSubroutineName: (Code) RETURN

Example

MySubroutine:
    DEBUG "Hello there!", CR
    DEBUG "This is a subroutine", CR
RETURN

To call and execute a subroutine you use the GOSUB keyword: :: Main: DEBUG "We're inside Main... Calling MySubroutine", CR GOSUB MySubroutine END

MySubroutine:

DEBUG "Hello there!", CR DEBUG "This is a subroutine", CR

RETURN

Calculating the area of a square

We can use variables within subroutines like so: :: sideLength VAR WORD result VAR WORD

Main:

sideLength = 50 GOSUB calcSquareArea

sideLength = 75 GOSUB calcSquareArea

sideLength = 100 GOSUB calcSquareArea

END

calcSquareArea:

DEBUG DEC "Calculating Area with side legnth: ", sideLength, CR result = sideLength * sideLength ' area = l x w DEBUG DEC "Result: ", result, CR

RETURN

Conclusion

Subroutines are a good way to organize and cleanup your code. If you have parts where you need to constantly repeat yourself than put it into a subroutine! There is no limit to how many times you can call a subroutine.

Practice

Create a movement sequence again but this time using subroutines. You should notice you're code should look a lot cleaner this time around.