Transcript Chapter 2 Primitive Data Type and Operations

Chapter 2 Primitive Data Types
and Operations
§2.1 Simple Programs
§2.2 Variables and Constants
§2.3 Primitive Data Types
§2.4 Number Operations
§2.5 Numeric Type Conversions
§2.6 Character Data Type
§2.7 Case Studies
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1
Objectives
To know the structure of simple C++
programs
 To know the concept of identifiers, variables,
constants
 To learn the use of assignment statements
and expressions
 To learn primitive data types

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§1.1 Simple Programs
Listing 2.1 Computing the Area of a Circle
#include <iostream>
int main() {
double radius;
double area;
// Step 1: Read in radius
(Including header files)
(Declaration of the main
function)
(Declaration of variables)
radius = 20;
(Comments)
// Step 2: Compute area
(Body statements)
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area = radius * radius * 3.14159;
// Step 3: Display the area
std::cout << "The area is ";
std::cout << area << std::endl;
}
ComputeArea
Run
3
Trace the Execution
allocate memory
for radius
#include <iostream>
int main() {
double radius;
double area;
radius
no value
// Step 1: Read in radius
radius = 20;
// Step 2: Compute area
area = radius * radius * 3.14159;
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// Step 3: Display the area
std::cout << "The area is ";
std::cout << area << std::endl;
}
4
Trace the Execution
#include <iostream>
int main() {
double radius;
double area;
// Step 1: Read in radius
radius = 20;
memory
radius
no value
area
no value
allocate memory
for area
// Step 2: Compute area
area = radius * radius * 3.14159;
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// Step 3: Display the area
std::cout << "The area is ";
std::cout << area << std::endl;
}
5
Trace the Execution
assign 20 to radius
#include <iostream>
int main() {
double radius;
double area;
radius
area
20
no value
// Step 1: Read in radius
radius = 20;
// Step 2: Compute area
area = radius * radius * 3.14159;
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// Step 3: Display the area
std::cout << "The area is ";
std::cout << area << std::endl;
}
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Trace the Execution
memory
#include <iostream>
int main() {
double radius;
double area;
// Step 1: Read in radius
radius = 20;
radius
area
20
1256.636
compute area and assign it
to variable area
// Step 2: Compute area
area = radius * radius * 3.14159;
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// Step 3: Display the area
std::cout << "The area is ";
std::cout << area << std::endl;
}
7
Trace the Execution
memory
#include <iostream>
int main() {
double radius;
double area;
radius
area
// Step 1: Read in radius
radius = 20;
20
1256.636
print a message to
the console
// Step 2: Compute area
area = radius * radius * 3.14159;
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// Step 3: Display the area
std::cout << "The area is ";
std::cout << area << std::endl;
}
8
Reading Input from the Keyboard
std::cin
An object to read input from the standard
input device, i.e. keyboard.
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ComputeArea1
Run
9
§1.2 Variables and Constants

Identifier

A sequence of characters that consists of



And start with a letter or an underscore (digit? No!).
An identifier can be of any length in C++ standard


letters, digits, and underscores (_),
but your C++ compiler may impose some restriction. Use
identifiers of 31 characters or fewer to ensure portability.
Reserved word



A special word that predefined in the language’s formal
specifications
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It cannot be used as a013225445X
user-defined name
Data type names, code construct labels, etc.

See Appendix A for a list of reserved words
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Namespace

What is std? The “standard” namespace


std::cout, std::endl, and std::cin
Namespace
A container of a group of identifiers
 To resolve potential naming conflicts


Two special namespaces
The global namespace: the default one
 std: the namespace of C++ standard


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std
Namespace is hierarchical
Global
A
B
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Namespace

How to use namespace
Add prefix to every reference:
std::cout<<“Hello”;
 Add an overall statement:
using namespace std; //use the whole space
using std::cout;
//use the specific identifier


How to declare namespace
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namespace X {
int i;
double j;
}
int main() {
X::i++;
}
ComputeArea2
Run
12
Variables

Variable


an identifier standing for a value that may vary
Three elements
name,
 type, and
 value

// Compute the first area
radius = 1.0;
area = radius * radius * 3.14159;
std::cout << area;
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// Compute the second area
radius = 2.0;
area = radius * radius * 3.14159;
std::cout << area;
13
Declaring Variables
int x;
// Declare x to be an
// integer variable;
double radius; // Declare radius to
// be a double variable;
char a;
// Declare a to be a
// character variable;
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Assignment Statements
x = 1;
// Assign 1 to x;
radius = 1.0;
// Assign 1.0 to radius;
a = 'A';
// Assign 'A' to a;
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Declaring + Initializing
int x = 1;
double d = 1.4;
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Constants

Constant


A value that cannot be changed
Two kinds of constants
Named Constant
 Literal

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Named Constant

Named constant

An identifier that stands for a constant, i.e.

The value of a named constant cannot be reassigned
const datatype CONSTANTNAME = VALUE;
const double PI = 3.14159;
const int SIZE = 3;
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Note: by convention, constants are
named in upper case.
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Literals

Literal


A constant value that appears directly in a
program
Numerical literals
40, 1.3

Character literals
‘a’, “a”, “this is”
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octal and hex Literals
Decimal: default one
 Octal: 0????
 Hexadecimal: 0x????

For example:
cout << 0xFFFF << " " << 010<<endl;
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§1.3 Primitive Data Types

4 primitive data types
Integer number
int, short, long
 Floating-point number
float, double, long double
 Character
 Void


符号位
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Modifiers

signed vs. unsigned
(10000001)2 或 10000001B
signed:
= -1
unsigned: = 129
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Numerical Data Types
Name
Synonymy
Range
Storage Size
short
short int
–215 (-32,768) to 215–1 (32,767)
16-bit signed
unsigned short
unsigned short int
0 to 216–1 (65535)
16-bit unsigned
–231 (-2147483648) to 231–1 (2147483647) 32-bit signed
int
unsigned int
signed
long
unsigned
0 to 232–1 (4294967295)
long int
unsigned long
float
unsigned long int
–231 (-2147483648) to 231–1 (2147483647) 32-bit signed
0 to 232–1 (4294967295)
32-bit unsigned
Negative range:
32-bit IEEE 754
-3.4028235E+38 to -1.4E-45
Positive range:
1.4E-45 to 3.4028235E+38
double
Negative range:
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-1.7976931348623157E+308 to -4.9E-324
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32-bit unsigned
64-bit IEEE 754
Positive range:
4.9E-324 to 1.7976931348623157E+308
long double
Negative range:
-1.18E+4932 to 3.37E-4932
Positive range:
3.37E-4932 to 1.18E+4932
Significant decimal digits: 19
80-bit
The length may be different for different compilers and computers
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The sizeof Function
sizeof: the unary operator used to calculate
the sizes of data types.
For example:
cout << sizeof(int)
<< " " << sizeof(long)
<< " " << sizeof(double);
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Floating-point Numbers

Floating-point numbers

Numbers with a decimal point
50.534  5.0534e+1


Various representations



its decimal point is moved (i.e., floated) to a new
position.
IEEE 754 Standard etc.
Float and double in C++
1.45 (double) 1.45f (float) 1.45F(float)
Precision of floating-point numbers
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Limited number of digits ->limited precision
Float type: 7 digits
1234.567342

Significant Random
digits
digits
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§1.4 Number Operations

Number operators
Name
Meaning
Example
Result
+
Addition
34 + 1
35
-
Subtraction
34.0 – 0.1
33.9
*
Multiplication
300 * 30
9000
/
%
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Division
1.0 / 2.0
0.5
Remainder
20 % 3
2
25
Integer Division
+, -, *, /, and %
5/2
yields an integer 2.
5.0/2 yields a double value 2.5
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5%2 yields 1 (the remainder of the division)
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Remainder Operator

Remainder is very useful



To determine whether a number is even or odd,
To determine some enumerable values,
…
Saturday is the 6th day in a week
A week has 7 days
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(6 + 10) % 7 is 2
The 2nd day in a week is Tuesday
After 10 days
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Example: Displaying Time
Listing 2.6: to convert number of seconds
to “hours + minutes”
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DisplayTime
Run
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Overflow and Underflow

Overflow, the condition that


a variable is assigned a value that is greater
than the maximum value in the value range.
For example:
short abc;
abc = 32767 + 1;
Underflow, the condition that

a variable is assigned a value that is smaller
than the minimum value in the value range.
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For example:
short value = -32768-1;
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Arithmetic Expressions
Straightforward translation from
mathematical expression
 The same operator precedence

3  4 x 10( y  5)(a  b  c)
4 9 x

 9( 
)
5
x
x
y
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(3+4*x)/5 – 10*(y-5)*(a+b+c)/x + 9*(4/x + (9+x)/y)
Operator
Operand
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Example: Converting Temperatures
Listing 2.7: to convert a Fahrenheit degree to
Celsius using the formula:
celsius  ( )( fahrenheit 32)
5
9
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FahrenheitToCelsius
Run
31
Shorthand Operators
Operator Example
Equivalent
+=
i += 8
i = i + 8
-=
f -= 8.0
f = f - 8.0
*=
i *= 8
i = i * 8
/=
i /= 8
i = i / 8
%=
i %= 8
i = i % 8
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Increment/Decrement Operators
Operator
Name
Description
++var
Preincrement
Increments var by 1 and evaluates to the
new value in var after the increment.
var++
Postincrement
Evaluates to the original value in var and
increments var by 1.
Predecrement
Decrements var by 1 and evaluates to the
new value in var after the decrement.
Postdecrement
Evaluates to the original value in var and
decrements var by 1.
--var
var--
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Example: Increment and Decrement
int i = 10;
int newNum = 10 * i++;
i++
int i = 10;
int newNum = 10 * (++i);
++i
Same effect as
int newNum = 10 * i;
i = i + 1;
Same effect as
i = i + 1;
int newNum = 10 * i;
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Note: these operators makes expressions short but more complex.
Avoid using these operators in multiple times such as this: int k = ++i + i.
34
§1.5 Numeric Type Conversions
Consider the following statements:
short i = 100;
long k = i * 3 + 4;
double d = i * 3.1 + k / 2;
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Values need to be converted to
different types
35
Conversion Rules

From a “smaller” type to a “larger” type
long double
double
float
unsigned long
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long
unsigned int
int
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Type Casting
The technique realizing type conversation
 Implicit casting

double d = 3;

Explicit casting

static_cast
static_cast<T>(v); //or
(T)v;
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--converts the value of the expression v to that of type T
int i = static_cast<int>(3.0);
37
Notes for Casting
1. Casting does not change the variable being
cast.
double d = 4.5;
int i = static_cast<int>(d); // d is not changed
2. The GNU C++ compiler will give a warning
when you narrow a type
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
Using static_cast to avoid such a warning
38
Example: Keeping Two Digits
After Decimal Points
Listing 2.8: to displays the sales tax with two
digits after the decimal point.
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SalesTax
Run
39
§1.6 Character Data Type

char
 the
data type for a single character
char letter = 'A';
char numChar = '4';

Read characters
cout << "Enter a character: ";
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cin >> ch;
40
Appendix B: ASCII Character Set
ASCII Character Set is a subset of the Unicode from \u0000 to \u007f
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Escape Sequences for Special Characters
Character Escape Sequence
Name
ASCII Code
\b
Backspace
8
\t
Tab
9
\n
Linefeed
10
\f
Formfeed
12
\r
Carriage Return
13
\\
Backslash
92
\'
\"
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Single Quote
39
Double Quote
34
42
Casting between Char and Numbers

The char type is treated as if it is an
integer of the byte size
int i = 'a'; // <==> int i = (int)'a';
char c = 97; // <==> char c = (char)97;

char type ~numeric types
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char c =0xFF41;//c is assigned to be (41)16
c=65
43
Notes

All numeric operators can be applied to char
operands.
int i = '2' + '3'; // (int)'2' is 50 and (int)'3' is 51
cout << "i is " << i << endl; // i is decimal 101
i is 101
int j = 2 + 'a'; // (int)'a' is 97
j is 99
cout << "j is " << j << endl;
99 is the ASCII code for c
cout << j << " is the ASCII code for " << (char)j << endl;

The ASCII for lowercase/uppercse letters are
consecutive integers starting from the code for
'a'/'A'.
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static_cast<char>('A' + (ch - 'a'))
char ch = 'a'; cout << ++ch;
44
§1.7 Case studies
Listing 2.9: to compute the monthly payment
and total payment
loanAm ount m onthlyInterestRate
1
1
numberOfYe ars 12
(1  m onthlyInterestRate)
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ComputeLoan
Run
45
Example: Counting Monetary Units
Listing 2.10: to convert amount in decimal
representing dollars and cents to a report listing
the monetary equivalent in single dollars,
quarters, dimes, nickels, and pennies.
$123.5 -> 123 dollars + 2 quarters
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ComputeChange
Run
46
Trace ComputeChange
Suppose amount is 11.56
int remainingAmount = (int)(amount * 100);
// Find the number of one dollars
int numberOfOneDollars = remainingAmount / 100;
remainingAmount = remainingAmount % 100;
remainingAmount
1156
remainingAmount
initialized
// Find the number of quarters in the remaining amount
int numberOfQuarters = remainingAmount / 25;
remainingAmount = remainingAmount % 25;
// Find the number of dimes in the remaining amount
int numberOfDimes = remainingAmount / 10;
remainingAmount = remainingAmount % 10;
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Introduction
C++the
Programming,
(c) 2007
Pearson Education, Inc. All rights reserved.
// Find the number
nickelsto in
remaining
amount
013225445X
int numberOfNickels = remainingAmount / 5;
remainingAmount = remainingAmount % 5;
// Find the number of pennies in the remaining amount
int numberOfPennies = remainingAmount;
47
Trace ComputeChange
Suppose amount is 11.56
int remainingAmount = (int)(amount * 100);
remainingAmount
// Find the number of one dollars
int numberOfOneDollars = remainingAmount / 100;
remainingAmount = remainingAmount % 100;
numberOfOneDollars
// Find the number of quarters in the remaining amount
int numberOfQuarters = remainingAmount / 25;
remainingAmount = remainingAmount % 25;
1156
11
numberOfOneDollars
assigned
// Find the number of dimes in the remaining amount
int numberOfDimes = remainingAmount / 10;
remainingAmount = remainingAmount % 10;
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Introduction
C++the
Programming,
(c) 2007
Pearson Education, Inc. All rights reserved.
// Find the number
nickelsto in
remaining
amount
013225445X
int numberOfNickels = remainingAmount / 5;
remainingAmount = remainingAmount % 5;
// Find the number of pennies in the remaining amount
int numberOfPennies = remainingAmount;
48
Trace ComputeChange
Suppose amount is 11.56
int remainingAmount = (int)(amount * 100);
remainingAmount
56
// Find the number of one dollars
int numberOfOneDollars = remainingAmount / 100;
remainingAmount = remainingAmount % 100;
numberOfOneDollars
11
// Find the number of quarters in the remaining amount
int numberOfQuarters = remainingAmount / 25;
remainingAmount = remainingAmount % 25;
remainingAmount
updated
// Find the number of dimes in the remaining amount
int numberOfDimes = remainingAmount / 10;
remainingAmount = remainingAmount % 10;
Liang,of
Introduction
C++the
Programming,
(c) 2007
Pearson Education, Inc. All rights reserved.
// Find the number
nickelsto in
remaining
amount
013225445X
int numberOfNickels = remainingAmount / 5;
remainingAmount = remainingAmount % 5;
// Find the number of pennies in the remaining amount
int numberOfPennies = remainingAmount;
49
Trace ComputeChange
Suppose amount is 11.56
int remainingAmount = (int)(amount * 100);
remainingAmount
56
// Find the number of one dollars
int numberOfOneDollars = remainingAmount / 100;
remainingAmount = remainingAmount % 100;
numberOfOneDollars
11
// Find the number of quarters in the remaining amount
int numberOfQuarters = remainingAmount / 25;
remainingAmount = remainingAmount % 25;
numberOfOneQuarters
2
// Find the number of dimes in the remaining amount
int numberOfDimes = remainingAmount / 10;
remainingAmount = remainingAmount % 10;
numberOfOneQuarters
assigned
Liang,of
Introduction
C++the
Programming,
(c) 2007
Pearson Education, Inc. All rights reserved.
// Find the number
nickelsto in
remaining
amount
013225445X
int numberOfNickels = remainingAmount / 5;
remainingAmount = remainingAmount % 5;
// Find the number of pennies in the remaining amount
int numberOfPennies = remainingAmount;
50
Trace ComputeChange
Suppose amount is 11.56
int remainingAmount = (int)(amount * 100);
remainingAmount
6
// Find the number of one dollars
int numberOfOneDollars = remainingAmount / 100;
remainingAmount = remainingAmount % 100;
numberOfOneDollars
11
// Find the number of quarters in the remaining amount
int numberOfQuarters = remainingAmount / 25;
remainingAmount = remainingAmount % 25;
numberOfQuarters
2
// Find the number of dimes in the remaining amount
int numberOfDimes = remainingAmount / 10;
remainingAmount = remainingAmount % 10;
remainingAmount
updated
Liang,of
Introduction
C++the
Programming,
(c) 2007
Pearson Education, Inc. All rights reserved.
// Find the number
nickelsto in
remaining
amount
013225445X
int numberOfNickels = remainingAmount / 5;
remainingAmount = remainingAmount % 5;
// Find the number of pennies in the remaining amount
int numberOfPennies = remainingAmount;
51
Example: Displaying Current Time
Listing 2.11: To display the current time in GMT in the
format hour:minute:second such as 1:45:19.
Hints: the time(0) function in the ctime header file returns
the current time in seconds elapsed since the time 00:00:00
on January 1, 1970 GMT.
Elapsed
time
Time
Current Time
Unix Epoch
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to C++ Programming, (c) 2007 Pearson Education, Inc. All rights reserved.
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01-01-1970
00:00:00 GMT
ShowCurrentTime
time(0)
Run
52
Summary
Structure of simple C++ programs
 Variables and constants
 Primitive data types and operations


Numeric data and character
Expressions
 Type casting

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