Divide by zero
Area of tube
TAs!


HtDP 4
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Computers deal with different situations... is the click on the demon or the shopkeeper? Was that a positive or negative number?

Consider:

Company XYZ & Co. pays all its employees $12 per hour. A typical employee works between 20 and 65 hours per week. Develop a program that determines the wage of an employee from the number of hours of work, if the number is within the proper range.

Math deals with true and false claims... these are the different booleans

We can create claims... ==, <, >, etc

We can combine claims... with and, or, or not

Functions can return booleans...
	 - isFiveHuh
	 - isBetween5and6Huh
	 - isBetween5and6OrOver10Huh

We can think of these as intervals on the number line

We can go back and forth

We can write programs that identify solutions to equations like
 - 6n + 3 = 12
 - 2n^2 = 74
 - 3n^2 + 2n + 11 = 19

These programs all /produce/ booleans. What about programs that /consume/ booleans?

When do we need this in the real world?

"Suppose the bank pays 4% for deposits of up to $1,000 (inclusive), 4.5% for deposits of up to $5,000 (inclusive), and 5% for deposits of more than $5,000."

if and else

information => data => examples

intervals mean there must be an if that decides which part of the interval the input comes from

our "take stock" part of the design recipe has a new step

sometimes we can simplify programs because we know earlier conditions are false