Control Flow

Table of Contents

2.1 - Boolean Values

2.2 - Logical Operators

2.3 - Conditional Statements

New Concepts

Sometimes we do not want our console to run through every single line of code. There are times when we want the computer to take different actions depending on some situation.

2.1 - Boolean Values

Boolean is a data type that can only be one of two values - true or false.

Comparison Operators

Operator	Name	Description	Example
==	Equal	Returns true if the operands match	3 == 3
!=	Not Equal	Returns true if the operands do not match	5 != 3
===	Strictly equal	Returns true if the operands match and are of same type	5 === 5
!==	Not strictly equal	Returns true if the operands do not match or aren’t of same type	6 !== "6"
<	Less than	Returns true if the left operand is less than the right operand	5 < 7
<=	Less than or equal	Returns true if the left operand is less than or equal to the right operand	4 <= 4
>	Greater than	Returns true if the left operand is greater than the right operand	5 > 2
>=	Greater than or equal	Returns true if the left operand is greater than or equal to the right operand	5 >= 4

2.2 - Logical Operators

Operator	Name	Description	Example
&&	And	Returns true if both the left operand AND the right operand are true	expr1 && expr2
||	Or	Returns true if either the left operand OR the right operand is true	expr1 || expr2
!	Negation	Returns true if the expression is true	!expr1

2.3 - Conditional Statements

Conditional statements are used to control a program to do different things depending on some condition. Some examples:

• IF you are feeling cold, THEN wear a sweater.
• IF the string contains more than 140 characters, THEN disable the "Tweet" button, ELSE keep the "Tweet" button enabled.

If Statements

To specify a block of code to be executed if a condition is true, we use an if statement.

if (condition) {
   block statement
}

For example:

var testGrade = "A";

if (testGrade == "A") {
   alert("Great job!");
}

Things to note:

• Conditions are in parentheses ()
• The block statement is in curly braces {}
• Expressions end with ; semicolons

Else Statements

We can also make the program execute some code if the condition is NOT met. To do so, we use an else statement.

var grade = "B";

if (grade == "A") {
   alert("Great job! Keep it up!");
} else {
   alert("Don't give up! Let's study more!");
}

What result will we get?

Else if Statements

We can make our if/else statements more specific by adding additional conditional statements using else if.

var grade = "B";

if (grade == "A") {
   alert("Great job! Keep it up!");
} else if (grade == "B") {
   alert("Not too bad!");
} else {
   alert("Don't give up! Let's study more!");
}

What result will we get here?

Important Note: The program goes through the code in order, meaning the order of your else if statements matter!

Activity: Grades

Write a series of if/else statements and use alert() to display the student’s test grade based on their test score. (How many different solutions can you come up with?)

Grade	Score
A	100 - 90
B	89 - 80
C	79 - 70
D	69 - 60
F	Below 60