Chapter 3 – Variables and Arithmetic Operations

Variable Rules

Must declare all variable names– List name and type

Keep length to 31 characters– Older compiler restriction

Give numeric values to variables with assignment statement

Lesson 3.1

variable_name = value;assignment operator

Naming Identifiers

First character must be letter– a-z, A-Z or _

Other characters– letters (a-z, A-Z, _ ) or digits 0-9

Cannot use C++ keywords (reserved words) Cannot have blank within identifies

Lesson 3.1

Keywords

Words with special meaning to C++ Also includes alternative representations of

certain operators and punctuators Full listing in Table 3.1 Examples:

– auto, bool, float, inline, union, delete– namespace, private, void

Lesson 3.1

Declaring Variables

Variables MUST be declared List name and data type Variables of same type may be declared in

same statement (separate by comma) Causes C++ compiler to know size of space

to be reserved for storing variable’s value

Lesson 3.1

double radius, diameter;data type variable namesseparator

Assignment Statements

Causes value to be stored in variable’s memory cell

variable_name = value; Variable name MUST appear on left Equal sign is assignment operator

Note: be careful = does NOT mean equal Example: temperature = 78;

Lesson 3.1

Constant Qualified Variables

Use const qualifier

const double PI = 3.14159; Cannot modify later in program Style tip: use all uppercase characters to

name constant– Makes constants easy to identify

Lesson 3.2

Formatting Output

Insert I/O manipulators (parameterized) into cout statements for printing– declared in header iomanip

#include <iomanip> Basic form

cout << manipulator(parameter);

what manipulator uses to modify output

Lesson 3.2

Listed in Table 3.2

setw( )

Sets field width Right justifies contents C++ automatically expands if set width too

small

Lesson 3.2

cout<<“number =“<<setw(7)<<num<<endl;

number = 5******* Field size

setprecision( )

Sets number of digits after decimal point All digits retained in memory Once set may or may not be used until

another statement changes it (compiler)

Lesson 3.2

num = 5.3415;cout<<“num = “<<setprecision(2)<<num;

num = 5.34

setfill( )

Specifies character for blank space in field Single quotes required around character

enclosed in parentheses

Lesson 3.2

num = 5.34;cout<<setw(10)<<setfill(‘*’)<<num;

******5.34

setiosflags(ios:: )

Perform number of different actions based on flag that is set

Table 3.3 Example:

Lesson 3.2

num = 5.34;cout<<setiosflags(ios::left) << setfill(‘*’)<<setw(10)<<num;

5.34******

left justifies in field

Printing “dollar” Format

Necessary to use I/O manipulators

Lesson 3.2

cout<<setprecision(2) <<setiosflags(ios::fixed|ios::showpoint) <<“Income = $” <<income;

Income = $7842.00

Character Data

Lowercase and uppercase characters Also graphic characters (!, #, ^) and “space” Escape characters (\n) regarded as single

characters Numbers 0-9 can also be characters Declare character variable: char c1,c2; Assign value: c1 = ‘g’;

Lesson 3.3

Can hold ONE characterEnclose in single quotes

Assigning Characters to int

C++ assigns ASCII code value for the char Does not use numeric value if assign 0-9

character Table 3.5 gives characters and ASCII

code/values

Lesson 3.3

Arithmetic Operations

Look like algebraic expressions Expression consists of sequence of

operand(s) and operator(s) – Operand (variable, constant, any value)– Operators (+, - , * , / , % )

Represent operation to be done Increment (++) and decrement (--)

Lesson 3.4

Problems

Uninitialized variables– C++ assigns own value– Does not trigger as an error

Exceeding integer range– int type range –32768 to 32767– Due to limit of two bytes of memory– Overflow error

Division by zero

Lesson 3.4

Pre- and Post- Operators ++ or -- Place in front, incrementing or decrementing

occurs BEFORE value assigned

Lesson 3.5

k = i++;

i = 2 and k = 1k = ++i;

Place in back, occurs AFTER value assigned

i = 2 and k = 1

k =--i;

k = i--;

i = i + 1;k = i;

33

i = i - 1;k = i;

11

k = i;i = i + 1;

13

k = i;i = i - 1;

21

Mixed Type Arithmetic Assign real to int

– Cut off fractional part of real Assign int value to real

– Put decimal point at end, converts method of storage to exponential binary form

Modify with cast operators– Change type of expression– Keyword static_cast– Old form: (type) expression

Lesson 3.5

static_cast Operator

General form

Lesson 3.5

static_cast <type> (expression)

Keyword requires underscore Expression for which temporary copy is

made of type type Type can be any valid C++ data type

Operator Precedence

Lesson 3.5

( ) parentheses unary prefix L to R 1++, -- post-(in/de)crement unary postfix L to R 2++, -- pre-(in/de)crement unary prefix R to L 3+ positive sign unary prefix R to L 3- negative sign unary prefix R to L 3static_cast cast unary prefix R to L 4%, *, / remainder/multi/div binary infix L to R 5+, - add/subtract binary infix L to R 6+=, -=, *= math & assignment binary infix R to L 7/=, %= math & assignment binary infix R to L 7= assignment binary infix R to L 7

Real data types

Decimal numbers float

– 4 bytes of memory, 6 digit precision double

– 8 bytes of memory, 15 digits precision long double

– 10 bytes of memory, 19 digits precision

Lesson 3.6

Integer data types Whole numbers int, signed int, short int, signed short int

– 2 bytes, range: -32768 to 32767 unsigned int, unsigned short int

– 2 bytes, range: 0 to 65535 long int, signed long int

– 4 bytes, range: -2147483648 to 2147483645 unsigned long int

– 4 bytes, range: 0 to 4294967295

Lesson 3.6

Math Functions

Need cmath or cstlib headers

#include <cmath> or #include <cstlib> General form: name(parameters) Note what type and form parameters take

– Trig functions use radian measure not angle Table 3.11 lists math library functions

Lesson 3.6

Summary

Declare variables and constants Format output Work with character data Create mathematical expressions Work with mixed data types and casting Use different data types for precision Utilize available math functions

Chapter 3

Learned how to: