Types
Chapter 2
Objectives
Observe types provided by C++
• Literals of these types
Explain syntax rules for identifier names
Study variables and constants
•
•
•
•
What they are
How they differ
How to declare
How to use
Investigate internal representations
First look at class attribute variables
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Problem
We are given the task of writing a program to
help the payroll office.
They compute pay for university student
workers
Students are all paid an hourly rate of
$6.75
Consider what behavior we
desire for the program.
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Behavior
For student payroll calculation:
Enter student name (last, first, initial): Smart, Osgood J.
Enter ID number: 123456
Enter hours worked: 9.99
Student: Osgood J. Smart
ID: 123456
Pay = $99.99
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Operations
Display string (prompts, labels, name)
Read a string (lastName, firstName)
Read a char (middleInitial)
Read an integer (idNumber)
Read a real value (hoursWorked)
Compute pay = hoursWorked *
HOURLY_WAGE
Display an integer (idNumber)
Display a real value (pay)
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Algorithm
1. Declare the constant HOURLY_WAGE.
2. Display to cout a prompt for the student’s name (last,
first, middle initial).
3. Read two strings and a character from cin into
lastName, firstName, middleInitial.
4. Display to cout a prompt for the student’s id number.
5. Read an integer from cin into idNumber.
6. Display to cout a prompt for the student’s hours.
7. Read a real value from cin into hoursWorked.
8. Compute pay = hoursWorked * HOURLY_WAGE.
9. Display firstName, lastName, middleInitial,
idNumber, and pay, with descriptive labels.
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Coding, Execution, Testing
Create a program stub
• Opening documentation
• Compiler directives for library includes
• An empty main function
Convert each step of algorithm into code
• Add declaration for each object not already
declared
• Declaration includes object type and name.
Observe source code, Fig 2.1
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Types and Declarations
Fundamental Types
Integers (whole numbers, negatives)
• int
Integer variations
• short, long, unsigned
Reals (fractional numbers)
• float, double, long double
Characters (letters, digits, symbols, punctuation)
• char
Booleans (logical values, true and false)
• bool
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Integer
Memory used for an int depends on word
size used by the hardware
• Usually 16, 32, or 64 bits used
16 Bits (2 bytes) – short int
• Range -32768 … 32767
32bits (4 bytes) – long int (or long)
• Range -2137483648 … 2137483647
One bit used for the sign
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Integer
Integers can be specified as unsigned
• Then the sign bit not needed
• Gives larger positive range
unsigned short (16 bits)
• Range 0 … 65535
unsigned long (32 bits)
• Range 0 … 4294967295
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Reals
float
• Usually a 32-bit value (4 bytes)
double
• A 64-bit value (8 bytes)
long double
• A 96- or 128-bit value
The programmer should
choose which type based on
degree of precision desired
for the object
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Reals
Values are stored internally in scientific
notation
1.23 10
•
•
•
•
4
A sign for the number
Significant digits of the number
The power of 10
Sign for the power
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Reals
Literal values
• A sequence of digits with leading sign,
containing a decimal point
• Scientific notation – any one of the following
forms
0.12e11
1.2E10
12.0E9
12.e9
12E9
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Characters
char type
Represents individual characters
• See ASCII character set in Appendix A
Characters represented in memory by
numeric values
Character literals
• Characters enclosed in single quotes
'X'
'7'
'>'
'e'
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Characters
Escape characters
• A backslash \ combined with another character hold
special meaning
Character
C++ Escape Sequence
Newline
\n
Horizontal tab
\t
Vertical tab
\v
Backspace
\b
Carriage Return
\r
Form Feed
\f
Alert (beep)
\a
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Strings
Related to characters
• A sequence of characters
• Enclosed in double quotes
"Hi Mom"
• Can include escape characters
"\nThe answer is "
Warning
• "A" is a string literal
• 'A' is a character literal
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Identifiers
C++ is case sensitive
• firstName is not the same as firstname
Typical usage
• Constants are all caps PI
• Variables
• Start with lower case
• Capitalize first letter of successive words
monthlyElectricCharge
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Object Categories
There are three kinds of objects:
Literals:
• unnamed objects
• having a value
• (0, -3, 2.5, 2.998e8, ‘A’, “Hello\n”, ...)
Variables:
• named objects
• values can change during program execution
Constants:
• named objects
• values do not change during program execution
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Literals
int literals are whole numbers:
-27, 0, 4, +4
double literals are real numbers, and can be:
• fixed-point: -0.333, 0.5, 1.414, ...
• floating-point: 2.998e8, 0.2998e9, ...
There are just two bool literals: false, true
char literals are single ASCII characters:
‘A’, ‘a’, ‘9’, ‘$’, ‘?’, ...
string literals are ASCII character sequences:
“Hello”, “Goodbye”, “Goodbye\n”, ...
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Constants
Declaration of software objects that remain
constant
const double HOURLY_WAGE = 6.75;
Rules
• const is a keyword
• Specify type
• Specify the name (caps recommended)
• Must be initialized with value at declaration
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