Library routines and maintainable programs

The library routines

• MOD(x, y): the remainder when x is divided by y.
• DIV(x, y): how many whole times y goes into x.
• ROUND(x, places): x rounded to that many decimal places.
• RANDOM(): a random number from 0 to 1 inclusive.

DECLARE Eggs, Boxes, Spare : INTEGER
OUTPUT "How many eggs?"
INPUT Eggs
Boxes <- DIV(Eggs, 6)
Spare <- MOD(Eggs, 6)
OUTPUT Boxes, "full boxes and", Spare, "eggs left over"
OUTPUT "Average per box:", ROUND(Eggs / 6, 1)

Random numbers in a range

RANDOM() gives a value from 0 to 1, so it is scaled up to the range needed. For a whole number from 1 to 6, multiply by 5 to get 0 to 5, round to a whole number, then add 1: ROUND(RANDOM() * 5, 0) + 1.

Making a program maintainable

• Meaningful identifiers: names like TotalPrice say what a value is; names like x don’t.
• Comments: explain what a section does and why, not every line.
• Procedures and functions: split the program into named parts that can each be tested and changed on their own.
• Constants: put fixed values like a tax rate in one named place.