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Selection Victor Norman CS104 Calvin College

New type: bool Stands for Boolean (named after George Boole) Two values: True and False Operations: –and, or, not – equality ( == ), inequality ( != )

Booleans necessary for “testing” You “constantly” are making decision: – if something is true, I’ll do this, otherwise, I’ll do that. – Code is similar. if something < somethingelse: – something < somethingelse is a boolean expression: produces True or False. if something == 0: – True if something evaluates to the value 0, False otherwise. Can be used in assignments: – witch = (she == duck) # witch has value True or False.

Boolean operators > etc:, =, ==, != Logical Operators: and or not

Clicker Questions

if Statement Syntax if : if : else:

Chained Conditionals if : elif : elif : else: # optional!

Example of use Suppose you have a function called turnDegrees(deg) which takes a positive or negative value in deg. You want to turnLeft() if deg is positive, turnRight() if negative, and do nothing if 0. How would you write this code? if deg > 0: # this code in turnDegrees() turnLeft(deg) elif deg < 0: turnRight(-1 * deg)

Nested conditional Q: Write code that prints the word “odd” or “even” depending on the value of variable anInt, and also prints “greater than 10” if the odd number has a value greater than 10. A: if anInt % 2 == 0 : print "even” else: print "odd” if anInt > 10: print "greater than 10”

Clicker Question if temperature > 0: print("above freezing") elif temperature == 0: print("at freezing") else: print("below freezing") Does the code below do exactly the same thing as the code above? (Assume temperature already refers to some numeric value.) if temperature > 0: print("above freezing") elif temperature == 0: print("at freezing") elif temperature < 0: print("below freezing")

Clicker Question age | experience: 0 | 1-2 | 3+ ------------------------------------------------- under 18 | \$6.50 | \$9.50 | \$11.00 18 and over | \$6.50 | \$12.00 | \$12.00 if experience == 0: wage = 6.5 elif (1) : if (2) : wage = 9.5 else: wage = 11 else: wage = 12

Assignment Do ~60 questions in CodeLab. Very good practice!