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
variable_name = value;
assignment operator
Lesson 3.1
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
data type double radius, diameter; variable names
separator
Lesson 3.1
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
temperature = 78;
 Example:
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);
Listed
in Table
what
manipulator
uses3.2
to modify output
Lesson 3.2
setw( )
 Sets
field width
 Right justifies contents
 C++ automatically expands if set width too
small
cout<<“number =“<<setw(7)<<num<<endl;
number =
5
*******
Field size
Lesson 3.2
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)
num = 5.3415;
cout<<“num = “<<setprecision(2)<<num;
num = 5.34
Lesson 3.2
setfill( )
 Specifies
character for blank space in field
 Single quotes required around character
enclosed in parentheses
num = 5.34;
cout<<setw(10)<<setfill(‘*’)<<num;
******5.34
Lesson 3.2
setiosflags(ios:: )
 Perform
number of different actions based
on flag that is set
 Table 3.3
 Example:
left justifies in field
num = 5.34;
cout<<setiosflags(ios::left)
<< setfill(‘*’)<<setw(10)<<num;
5.34******
Lesson 3.2
Printing “dollar” Format
 Necessary
to use I/O manipulators
cout<<setprecision(2)
<<setiosflags(ios::fixed|ios::showpoint)
<<“Income = $” <<income;
Income = $7842.00
Lesson 3.2
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’;
Can hold
ONEincharacter
Enclose
single quotes
Lesson 3.3
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
Lesson 3.4
by zero
Pre- and Post- Operators
 ++
or - Place in front, incrementing or decrementing
occurs BEFORE value assigned
i = 2 and k = 1
k = ++i;
i = i + 1; 3
k = i; 3
 Place
i = i - 1; 1
k = i; 1
in back, occurs AFTER value assigned
i = 2 and k = 1
k = i; 1
k = i++;
i = i + 1; 3
Lesson 3.5
k =--i;
k = i--;
k = i; 2
i = i - 1; 1
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
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
Lesson 3.5
Operator Precedence
( )
++, -++, -+
static_cast
%, *, /
+, +=, -=, *=
/=, %=
=
Lesson 3.5
parentheses
post-(in/de)crement
pre-(in/de)crement
positive sign
negative sign
cast
remainder/multi/div
add/subtract
math & assignment
math & assignment
assignment
unary
unary
unary
unary
unary
unary
binary
binary
binary
binary
binary
prefix
postfix
prefix
prefix
prefix
prefix
infix
infix
infix
infix
infix
L to R
L to R
R to L
R to L
R to L
R to L
L to R
L to R
R to L
R to L
R to L
1
2
3
3
3
4
5
6
7
7
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
Lesson 3.6
3.11 lists math library functions
Summary
Learned how to:
 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