Variables and Constants

1
Chapter 3

• Variables and Constants

2
3.1 Using Variables

• A named memory location
• Stores a value
• Defined by type and identifier
• Kind
• Name
• double Radius

type
identifier
3
assignment

• Give a variable a value
• Equal sign ()
• double Radius
• double Radius 10
• double Radius 12.3

?
10
12.3
4
assignment statement structure

• variable name value
• Area 3.14 10 10
• Assignment Complete Review 1 and 2 on
• p. 3-3.

5
3.2 Obtaining a Value from a User

• cin console input stream (iostream library)
• pauses a program, allows user to enter a number
• cin gtgt Radius

get from operator extraction operator
6
3.3 Using Named Constants

• const (type ) (an identifier) (value)
• Represents a value that does NOT change
• const double PI 3.14
• cout ltlt Area ltlt (PI Radius Radius)

7
3.4 Choosing Identifiers

• Must start with a letter.
• Must contain only letters, digits, and the
  underscore (_).
• Can be of any length.
• Are case-sensitive.
• Cannot be a keyword (C reserve word).
• Quickly and clearly understandable.

8
3.5 Built-In Data Types
9
double

• store positive or negative real numbers
• floating number
• double j
• j 123456789.0
• cout ltlt j ltlt endl
• Displays 1.23457e08

10
int and long

• Store positive and negative integers
• Difference between two, range
• int i
• i 12.9
• cout ltlt i ltlt endl
• Displays 12

11
char

• Stores a single character.
• Requires single-quotation marks.
• char ch
• ch A
• cout ltlt ch ltlt endl
• Displays A

12
3.6 Variable Definitions

• Can be defined in single statements.
• Can define multiple variables of the same type in
  a single statement.
• int x, y, z
• char ch1, ch2

13
3.6 Variable Definition contd

• Can also include assignment.
• double x 6
• char ch1 A ch2 B
• int y 2x

14
3.7 Expressions and Operators

• Multiplication (), addition (), subtraction
  (-), and division (/) (NOTE no standard operator
  for exponentiation in C)
• promotion C promotes the value with the
  narrower range (the integer) to the type of the
  value with the wider range (the double).

15
Integer Division

• truncates the decimal portion of the quotient to
  result in an integer
• An expression involving only integers results
  in an integer
• cout ltlt (25/4) // Displays 6

16
typecasting

• Converts the type of one value into a real
  number.
• cout ltlt (double(25)/4)
• Displays 6.25 because C promotes the 25 to a
  double and then real number division is performed.

17
modulus division

• Returns the remainder resulting from division.
• cout ltlt (254) //Displays 1
• 25/4 6R1
• Useful in examing the digits of number, finding
  the number of minutes left over after hours have
  been account for.
• May only be used with int or long values

18
operator precedence

• Specific order of operations
• 1 parenthesis
• 2 multiplication, division, modulus
• 3 addition, subtraction
• Note operators of the same precedence are
  evaluated left to right.

19
3.8 The string Library

• A sequence of characters, like a message or name.
• include ltlvp\spring.hgt
• Takes input to the first blank.

20
getline

• Requires the first item in parentheses to be the
  name of the input stream
• Second item, name of the string variable.
• getline(cin, Name)

21
string variable assignment

• Can be assigned values like other variables
• Name Fedor
• concatenation joining of two strings.
• cout ltlt (FirstName LastName)

22
3.10 Output Formatting

• Useful for lining up numbers.
• Statement is required for each item output.
• cout.width(10) cout ltlt 123 ltlt endl
• cout.width(10) cout ltlt 12 ltlt endl
• cout.width(10) cout ltlt 12345 ltlt endl

23
setf()

• default output is right aligned.
• cout.setf(iosleft)

24
precision()

• cout.setf(iosfixed) // fix num of decimals
• cout.precision(3) // set number of dec to 3