1. C++ Data Types Data Type
A key capability of a programming language
Establishes both the type of information that can be stored as well as operations that can be done on that information
C++ has built-in support for 3 major data types:
Numerical, Alphabetic, and Logical
Numerical: Integers and floating point
Alphabetic: character (and string)
Logical: true or false
These can be used to save information of the given type by setting aside a memory location to store the information under a user defined name

2. Numerical Data Two broad categories Integers store “whole” numbers
No fractions or decimals
positive and negative “counting” numbers, incl. zero
Three types: short, int, long
Floating point numbers
“Fractional” numbers (i.e. those with decimal points)
Two main types: float and double
Can be represented in either decimal or scientific notation
Decimal:
Scientific 2.75e3 (mantissa and exponent) – same as 2.73x103

3. Alphabetic Data Character data Strings data
Store a single alphanumeric character
Type is char
characters are represented in single quotes: ‘x’, ‘A’, or ‘=‘
Strings data
Store a “string” of characters, like a name
Type is string – specified in double quotes: “John” or “apple”
Not built-in, comes from a pre-defined library (distributed with C++)
It is actually a class (which did not exist in the original C language)
To use strings, must include the string library: #include <string>

4. Logical Data Boolean Named for George Boole
English mathematician (mid 1800’s) – developed Boolean Algebra
Type is bool – used to represent conditional values
Supports only two values: true and false
Note: true and false are not strings – no quotes!

5. Variables/Identifiers
To store information of a given type, a variable (identifier) of that type must be declared
The type must be specified
A name for the variable must be declared
An initial value may, optionally, be assigned
type name[=value], [name2=value2], …;
Multiple variables can be assigned in one statement
Separated with commas

6. Valid variable names Rules
Can only contain letters, numbers, and underscore (_)
Good: name, x, abc123, last_name
Bad: last-name
Cannot begin with a number
Bad: 1letter
Cannot be a C++ reserved word
Bad: float, int, main
Is case-sensitive
Name is not the same as name

7. Variable Declaration Examples
int i; // variable (no initialization) int j, k, l; // multiple variables int n=10; // variable with initialization float x, pi= ; // init and no init char a= ’A’; string name= ”John”; bool maybe= true;

8. const qualifier
Variables (as the name implies) store information that can be changed in a program
Occasionally, it is desirable to disallow changes to stored information
Use keyword const
const type name=value, name2=value2, …
Error message if an attempt is made to change a const variable
const variables must be initialized on declaration (since they can’t be changed)
const float pi= ;

9. Compiler Directive Another way to define a fixed (constant) value
Syntax:
#define NAME value
Example:
#define PI
Note – there is NO semicolon “;” after the declaration
Because this is actually interpreted in a pre-compilation step
“NAME” gets replaced globally in the program before the actual compilation occurs
Accepted practice is to capitalize compiler directives

10. Integers Can store positive and negative integers Three types
No decimals!
Three types
short, int, long
Usually representing different numerical ranges
We will be using int primarily
Ranges are compiler dependent
Generally: short <= int <= long
On our system, int can store values between and
(approx. +/- 2 billion)

11. Floating Point Numbers
Stores numerical data with decimals
Two types
float and double
We will be using float primarily
Ranges are compiler and system dependent - on ours:
float can store pos and neg values between 1e-38 and 1e38 (approx.)
float has 6 decimal digits of precision
double has much greater range and precision

12. Literals and the assignment operator
Literal is a term used to describe an explicit, fixed data value.
As opposed to a value that is the result of a computation (like z=x+y;)
Any data type can be assigned a literal value
Using the assignment (=) operator – i.e. the equals operator
integer assignment
int i, j, k; // declare 3 integers
i= 10;
j= 0;
k= -23;
10, 0 and -23 are literals

13. Floating point Literals
Scientific Notation
Two parts
Mantissa – the decimal number before the “e”
Exponent – the characteristic (exponent) is the integer after the “e”
number= mantissa x 10characteristic
Floating point data
float x, y, z; // declare 3 floating point variables
x= ; // decimal notation
y= 3.2e5; // scientific notation
z= -15e-10;
Numerical values above are floating point literals

14. Literals cont. char Examples string Examples bool
A single character enclosed in single quotes
Examples
char a, b, c; // declare 3 chars
a= ‘A’;
b= ‘v’;
c= ‘?’;
‘A’, ‘v’, and “?” are character literals
string
One or more characters enclosed in double quotes
Examples
string name; // declare a string
name= “John”;
“John” is a string literal
bool
true or false (no quotes!)
bool maybe=true;

15. Data/Variable Storage
Counting in Binary 1 2 10 3 11 4
100 5
101 6
110 7
111 8
1000 … -
255
Data stored in memory
Each memory location has a numerical address
Each location can store one byte of information
One byte is 8 bits
One bit can store one binary digit (0 or 1)
So, a byte can store 28 unique values (256 values)
Number of bytes required to store information will depend on the type of data being stored

16. Typical data storage by type
Data Storage examples
Type
# of bytes/bits
int
4/32
short
2/16
long
8/64
float
double
char
1/8
string
N/(N*8)
bool
Type
Name
Memory Address
value
int n
1000 10
1001
1002
1003
char a
1004
‘A’
string
name
1005
‘J’
1006
‘O’
1007
‘H’
1008
‘N’
bool
maybe
1009
true
float pi
1010
1011
1012
1013
int n=10;
float x, pi= ;
char a=’A’;
string name=”John”;
bool maybe= true;

17. Variables “under the hood”
For each variable, compiler needs to keep track of 4 pieces of information:
Variable name
Location of data
Memory address of stored data
Variable type
How to interpret data
How many bytes?
Value
Stored at the memory address
Memory locations … ?
0x1000
0x1001
0x1002
0x1003
0x1004
0x1005
float pi= ;
Variable
Name pi
Location
0x1001
Type
float