Conditionals

2.  True or False?
 Boolean values are abstract concepts used in
computations.
 TRUE!
 Named in honor of George Boole who invented
a system of mathematics in which the abstract
concepts of true and false can be used in
computations

3.  Sometimes a program needs to ”decide” whether
or not to execute certain instructions
 All previous instructions have been consecutive
(sequence structure), that is:
 One
 After
 The
 Other
 in the order that they
appear.
 Now we can add some variability, interactivity,
and dynamisms into our applications.

4.  A conditional is what we refer to as a decision
structure. A decision is made is based upon a set of
rules. We mainly will be working with the if…then.
 An If decision executes a set of instructions if a
Boolean condition is true
 Instruction tests a condition
 The condition controls how the
application executes
 Ex.
 If an event occurs then a certain
outcome will happen.
 If it rains, then I will wear a rain coat.

5.  Conditional arguments are Boolean expressions.
 We use relational operators to form Boolean
statements.
 Operator Meaning
 == equal to
 < less than
 <= less than or equals to
 > greater than
 >= greater than or equal to
 != not equal to
 Common Mistake: Confusing = with ==

6.  Code:
Creating a decision structure:
if (expression):
statement
 To execute more than one statement in a block they must be indented
equally:
if (score > 90):
grade = 'A'
print(“Good Job!n”)
print(“Not part of the conditions execution”)
 Good Programming: Commenting conditional blocks
 Common Mistakes: Forgetting equal indent, forgetting :, forgetting
space after if
 Good Practices: Use a tab not a space (easier to line up and
troubleshoot)
Space
Indent

8.  Code:
 Creating a button object
 GPIO.setup(pin# , GPIO.IN)
 Using button functions to determine if
triggered
 if (GPIO.input(pin#) == False):
Command
Command

9.  We can nest conditional statements to have several decisions
structures evaluated within one decision tree.
 This allows an application to check multiple situations for a
single desired outcome.
 With an if statement if it evaluates to true it is true the body
statements executed
 However, with an else it will execute when the if statement is
false
 If and else compliment each other
 50/50
 Two halves of the same coin
 Ie. If an event occurs then a certain outcome will happen, else do
something different.
 Ex.
 If it rains, then I will wear a rain coat, else I don’t need a jacket
 Flipping a coin. If it is heads I win, else it is tails I lose(100%
outcomes)

10.  Code:
Creating a nested decision structure:
if (expression):
statement
else:
statement
 Good Programming: Lining up the else with the
preceding if.
 Common Mistakes: Forgetting the : after the else