CS111 Lab Variables

Instructor: Michael Gordon

What is a variable?

Variables are a means of storing data for

the program.

Variables come in different types and

store different kinds of information:

Integers (whole numbers)

Decimal numbers

Characters

And more…

Common Types

int – a positive or negative integer

double – a positive or negative decimal

char – a single character

bool – a true or false value

string – a string of text

The above names are case sensitive

Int, Double, Bool, or Char won’t work

Declaring a variable

To declare a variable, you write its type

and its name (which you give it).

Examples:

int students; could be an integer variable

that stores the number of students in a class

string name; could store the class title

bool full; could store whether the class is full

or not

Assigning values

We use the equal sign to assign values to

a variable. Examples:

students = 30;

name = “CS111”;

full = false;

Strings must be contained within double

quotes.

char variables must be contained within

single quotes.

Initializing

Sometimes we declare variables and then

later assign their values, but sometimes we

want to give an initial value right away.

This is called initializing. Examples:

int students = 30;

string name = “CS111”;

bool full = false;

More on variable names

C++ rules for variable names:

Must start with a letter, not a number

Must have NO space in it

No special characters (only letters,

numbers, and underscore).

Must not be a C++ keyword, such as: return,

if, else, int, double, etc.

Variable initializations

Illegal examples

String name = 45;

int count = 2.5;

char grade = B;

double = ‘3.14’;

bool = “False”;

Legal examples

string name = “45”;

int count = 2;

char grade = ‘B’;

double = 3.14;

bool = False;