DECISION STRUCTURES

Review Conditionals 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.

Review Conditionals 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 ==

Code

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

SpaceIndent

if Statement Example

Reviewing If…Else 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)

CodeCreating 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?

if/else Example

If…ElIf 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

CodeCreating a nested conditional:

if (condition):Statement

elif (condition):Statement

elif (condition):StatementStatement

else: Statement

Common Errors: Not Lining up Else with its

preceding If. Question: Why is a trailing else good programming?

Nested if/else if Example

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

Nested if Statements