Conditionals

2.  A conditional is what we refer to as a decision
structure. Where a decision is made is based upon a
set of rules. We mainly will be working with the
if…then.
 Ie. If an event occurs then a certain outcome will
happen.
 Ex. If it rains, then I will wear a rain coat.

3.  Conditional arguments are Boolean expressions.
 Question: Meaning???
 We use relational operators to form Boolean expressions.
 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 ==

4.  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”)
 Good Programming: Commenting conditional blocks
 Common Mistakes: Forgetting equal indent, forgetting :,
and forgetting space after if
Space
Indent

6.  We can nest conditional statements to have
several decision structures within one statement.
 This allows an application to check multiple
situations for 1 desired outcome
 Allows us to simplify code by not having as
many separate if statements.
 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 not heads it must be tails(100% outcomes)

7. Creating a nested conditional:
 if (condition):
statement
else:
statement
 Good Programming: We usually line up else with
the preceding if to make it easier to find errors.
 Question: Be careful testing real numbers for
equality, why?

9.  We can nest conditional statements to have
several decision structures within one
statement in order to test various situations for
a desired result.
 Ie. If an event occurs then a certain outcome will
happen Or else if this happens do this or else do
something else
 We can nest as many ElseIf’s together but each set
of conditionals can have only one Else statement
otherwise it will create a logical error
 Ex.
 If it rains, then I will wear a rain coat else if it snows then I
will wear gloves or else I won’t need a jacket.
 Rolling a die 1,2,3,4,5,6 if lands on 1 don’t need to check
other sides b/c 100% of outcomes

10. Creating a nested conditional:
 if (condition):
Statement
elif (condition):
Statement
elif (condition):
Statement
Statement
else:
Statement
 Common Errors: Not Lining up Else with its preceding If.
 Question: Why is a trailing else good programming?

11. Question: What zodiac sign is it for the current year?