1. Types, Truth, and Expressions (Part 2)
Intro to Computer Science
CS1510
Dr. Sarah Diesburg

2. Line Wrap
Some rules
Strings must be closed in the line in which they start
Adding a backslash at the end of the line tells python that the command is continued on the end of the line

3. Review : Python if Statement
if <expression> :
suite
Evaluate the expression to a boolean value (True or False)
if True, execute all statements in the suite

4. Review : Warning About Indentation
Elements of the “suite” must all be indented the same number of spaces/tabs
Python only recognizes suites when they are indented the same “distance”
You must be careful to get the indentation right to get suites right.

5. Let’s test your knowledge
Let‘s look at #1-4 in my questions.py program…

6. Let’s test your knowledge
Problems #1-4 : Which letters are printed? A B
A and B
Neither

7. Let’s test your knowledge
Let’s look at statements with if, elif, else
Problems #5-9 : Which letters are printed? A B
A and B
Neither

8. Python Selection, Round 2
if boolean expression: suite1 else: suite2
The process is:
evaluate the boolean
if True, run suite1
if False, run suite2

9. Python Selection, Round 3
if boolean expression1: suite1 elif expression2: suite2
The process is:
evaluate expression1
if True, run suite1
If False, evaluate expression 2
if True, run suite2

10. Python Selection, Round 3
if boolean expression1: suite1 elif boolean expression2: suite2 #(as many elif’s as you want) else: suiteLast

11. if, elif, else, the Process
Evaluate boolean expressions until:
The boolean expression returns True
None of the boolean expressions return True
If a boolean returns True, run the corresponding suite. Skip the rest of the if
If no boolean returns True, run the else suite, the default suite

12. Compound Expressions
Logical Operators (lower case)
and or
not

13. Let’s test your knowledge
Problems #10-11 : Which letters are printed? A B
A and B
Neither

14. Truth Tables

15. Truth Tables

16. Truth Tables

17. Truth Tables

18. Truth Tables

19. Chained Comparisons You are going to be tempted to write:
0 <= myInt <= 5
But you will need to be very careful

20. Compound Evaluation
Logically 0 < X < 3 is actually (0 < X) and (X < 3)
Evaluate using X with a value of 2: (0< X) and (X< 3)
Parenthesis first: (True) and (True)
Final value: True
(Note: parentheses are not necessary in this case.)

21. Compound Evaluation BUT, I’ve seen students write: 3 < X < 0
Meaning they want to know if x is outside of that range.
But this is actually (3 < X) and (X < 0)
Evaluate using X with a value of 5: (3< X) and (X< 0)
Parenthesis first: (True) and (False)
Final value: False