Data Types & Variables Review

Data Types and Variables Review

Data types can be categorized as either primitive or reference

Primitive

Reference

Labelling

Label the following Data Types

(I know some can be "right" but it will make it wrong because it's a computer program, try to think of size order to help.)

Drag labels to their correct position on the image

boolean

short

char

byte

long

int

float

Array

double

String

Variables

A variable is a piece of the computer's memory that is given a name and a type, and can store a value.

State its name and type

Declare It

Store a value into it

Initialize It

Print it or use it as part of an expression.

Use It

​Steps for using a variable

Set aside memory for storing a value.

! Variables must be declared before they can be used

Syntax = type <name>;
*The name is an identifier

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Declaration

Multiple Choice

Which of the following properly DECLARES a variable?

• int x = 5

• byte y

• myGPA;

• float myGPA;

Storing a value into a variable

! can be done in one step OR separately

Syntax = name = expression;
int x; or int x = 3;
x = 3;

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Assignment

Multiple Choice

Which of the following properly ASSIGNS a variable?

• x = 5

• byte y = 2

• myGPA = 4.0;

• float myGPA = 4.0

Once given a value, a variable can be used in expressions

System.out.println("x is " + x);

! you can assign a value more than once

int x = 3; //here x is 3
x = 4 + 7; //now x is 11

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Using Variables

=
This is the assignment operator!
It does not mean equals, instead it means "stores the value of "

​

​NOT EQUALS!

​Multiple Variables

Multiple variables of the same type can be declared and initialized at the same time.

Syntax:
int x, y, z; //declares three integers
int a = 1, b = 2, c = 3; //declare and initialize three
// integers

double myGPA = 4;


hmmm... can you guess what's coming?

An int value can be stored in a double variable, but the value is converted to the equivalent type.

int x = 2.5; //ERROR


incompatible types

A variable can only store a value of its own type.

Assignment and Types

Math Response

What does this program print?

double myGPA = 4;

System.out.println(myGPA);

Type answer here

Correct Answer: 4.0

Deg^°

Rad

Poll

Does this cause an error?

int x;

7 = x;

• Yes

• No

Poll

Does this cause an error?

int x;

System.out.println(x);

• Yes

• No

Poll

Does this cause an error?

int x;

int x = 3;

• Yes

• No