3 – At a Crossroads

• Use relational operators to form logical expressions
• Use binary selection (if, else statements) to control the flow of program execution
• Generate and use random integers

• Selection
• relational operators,
• logical (or Boolean) expressions
• conditions

• randomness
• execution
• walk-through

Last lesson, you…

• Used arithmetic expressions to calculate values
• Used variables to store and reference values
• Followed walk-throughs of code and kept track of variable values
• Wrote programs that receive numerical input from the keyboard

In this lesson, you will…

• Use selection (if statements) to control the flow of program execution between branches
• Introduce elements of randomness into your programs

• Selection is when your programs check conditions and select the path of action that they will follow accordingly.

You will need an if or an if, else when there is more than one possible path for your program to follow.

• Download this lesson’s worksheet to your Home Drive.

• The condition will check if the value of user is equal to the string "Elizabeth".
• The expression user == "Elizabeth" will evaluate to either True or False.
• This is the if block, i.e. the code that will be executed if the condition is True.
• This is the else block, i.e. the code that will be executed if the condition is False.
• Only one of these blocks will be executed, depending on the value of the condition.

• It’s if and else. No capitals.
• A colon : is always required after the if condition and after else.
• Use indentation to indicate which statements ‘belong’ to the if block and the else block.
• The == operator checks for equality. The single = is only used in assignments.
• user is a variable. Don’t use quotes. "Elizabeth" is a string literal. It needs quotes.

Symbol	Meaning	Examples	Meaning
==	equal to	a == 1	Does a equal 1?
!=	not equal to	b != c	Are b and c different?
<	less than	d < 3	Is d less than 3?
<=	less than or equal to	d <= 3	Is d at most 3?
>	greater than	d > 10	Is d greater than 10?
>=	greater than or equal to	d >= 10	Is d at least 10?

• Expressions formed using these operators evaluate to either True or False.
• You can also use these operators to compare alphanumeric values (strings).

• You are going to make a program that asks for the user’s favourite film. The program will either react enthusiastically to one particular film or display a generic comment.
• Follow the instructions for Task 1 on your worksheet and complete the code on the trinket.io assignment to complete this task.

• This program picks a specific ‘lucky number’ and displays it to the user.
• Follow the instructions for Task 2 on your worksheet to complete the code below.
• Use the trinket.io assignment to complete this task.

In this lesson, you…

• Used selection (if statements) to control the flow of program execution
• Introduced elements of randomness into your programs

Next lesson, you will…

• Explore how selection can handle more than two possible branches
• Introduce iteration (while statements) to allow the flow of program execution to include loops

• Complete the Silver Task 1 – Film Critic and upload the worksheet to bournetolearn.com.

• Complete the Gold Task 2 – Lucky Number tasks in the worksheet.

• Complete the Platinum Task – Eligible to Vote in the worksheet.