C++ Programming: Program Design Including Data Structures, Second Edition

C++ Programming:Program Design Including Data

Structures, Second Edition

Chapter 8: User-Defined Simple Data Types, Namespaces, and the string

Type

C++ Programming: Program Design Including Data Structures, Second Edition expanded by J. Goetz, 2004

2

Objectives

In this chapter you will:

• Learn how to create and manipulate your own simple data type — called the enumeration type

• Become aware of the typedef statement• Learn about the namespace mechanism• Explore the string data type, and learn how to

use the various string functions to manipulate strings


3

Enumeration Type

• Data type - a set of values together with a set of operations on those values

• To define a new simple data type, called enumeration type, we need three things:

• A name for the data type

• A set of values for the data type

• A set of operations on the values


4

Enumeration Type (continued)

• The syntax for enumeration type is:

enum typeName{value1, value2, ...};

value1, value2, … are identifiers called enumerators

value1 < value2 < value3 <...

• A new simple data type can be defined by specifying its name and the values, but not the operations

• The values must be identifiers


5

Enumeration Type

• is an ordered set of values

• If a value has been used in one enumeration type

• It cannot be used by another in the same block

enum mathStudents{John, Bill, Lisa};

enum compStudents {Susan, John, william};

John is not allowed in the 2nd enum type

• The same rules apply to enumeration types declared outside of any blocks


6

Enumeration Types

• C++ allows creation of a new simple type by listing (enumerating) all the ordered values in the domain of the type

EXAMPLE

• Below JAN < FEB < MAR < APR , and so on

enum MonthType { JAN, FEB, MAR, APR, MAY, JUN,

JUL, AUG, SEP, OCT, NOV, DEC } ;

name of new type list of all possible values of this new type


7

Examples

• The following are illegal enumeration types because none of the values is an identifier:

enum grades{'A', 'B', 'C', 'D', 'F'};

enum places{1st, 2nd, 3rd, 4th};

• The following are legal enumeration types:

enum grades{A, B, C, D, F};

enum places{first, second, third, fourth};


8

Declaring Variables

• The syntax for declaring variables is:

dataType identifier, identifier,...;• The following statement defines an

enumeration type sports

enum sports{basketball, football, hockey,

baseball, soccer, volleyball};

• The following statement declares variables of the type sports.

sports popularSport, mySport;


9

Assignment

• The statement:

popularSport = football;

stores the word football into popularSport

• The statement:

mySport = popularSport;

copies the contents of the variable popularSport into mySport


10

Declaring enum Type Variables



MonthType thisMonth; // declares 2 variables

MonthType lastMonth; // of type MonthType

lastMonth = OCT ; // assigns values

thisMonth = NOV ; // to these variables...

lastMonth = thisMonth ;

thisMonth = DEC ; 10


11

Storage of enum Type Variables



stored as 0 stored as 1 stored as 2 stored as 3 etc.

stored as 11


12

Operations• No arithmetic operation is allowed on enumeration

types

• The following statements are illegal;

mySport = popularSport + 2; //illegal

popularSport = football + soccer; //illegal

popularSport = popularSport * 2; // illegal

• The increment and decrement operations are not allowed on enumeration types

• The following statements are illegal;

popularSport++; //illegal

popularSport--; //illegal


13

C++ Simple Data TypesC++ Simple Data Types

simple types

integral floating

char short int long bool enum float double long double

unsigned


14

More about enum Type1. Stream I/O ( using the insertion << and extraction >> operators

) is not defined for enumeration types. Instead, functions can be written for this purpose.• Input and output are defined only for built-in data types

such as int, char, double• The enumeration type can be neither input nor output

(directly)

2. Comparison of enum type values is defined using the 6 relational operators ( < , <= , > , >= , == , != ).

3. Enumeration type can be used in a Switch statement for the switch expression and the case labels.

4. An enum type can be the return type of a value-returning function in C++.


15

Operations and Input/Output

• Because an enumeration is an ordered set of values• We can use relational operators with them

• The cast operator can be used to increment, decrement, and compare values

popularSport = static_cast <sports> (popularSport +1);

popularSport++; //illegal

football <= soccer // is true


16

MonthType thisMonth;

switch ( thisMonth ) // using enum type switch expression{ case JAN :

case FEB :case MAR : cout << “Winter quarter” ;

break ;case APR :

case MAY :case JUN : cout << “Spring quarter” ;

break ; case JUL :case AUG :case SEP : cout << “Summer quarter” ;

break ; case OCT :

case NOV :case DEC : cout << “Fall quarter” ;

}

16


17

Functions and Enumeration Types

• Enumeration type can be passed as parameters to functions either by value or by reference

• A function can return a value of the enumeration type


18

Using enum type Control Variable with for Loop

enum MonthType { JAN, FEB, MAR, APR, MAY, JUN, JUL, AUG, SEP, OCT, NOV, DEC } ;

void WriteOutName ( /* in */ MonthType ) ; // prototype.. .

MonthType month ;

for (month = JAN ; month <= DEC ; month = static_cast <MonthType> (month + 1 ) )

{ // requires use of type cast to increment

WriteOutName ( month ) ; // function call to perform output .

}18


19

void WriteOutName ( /* in */ MonthType month )// Prints out calendar name corresponding to month// Precondition: month is assigned// Postcondition: calendar name for month has been written out

{ switch ( month ) {

case JAN : cout << “ January ” ; break ;case FEB : cout << “ February ” ; break ;case MAR : cout << “ March ” ; break ;case APR : cout << “ April ” ; break ;

case MAY : cout << “ May ” ; break ;case JUN : cout << “ June ” ; break ; case JUL : cout << “ July ” ; break ;case AUG : cout << “ August ” ; break ;case SEP : cout << “ September ” ; break ; case OCT : cout << “ October ” ; break ;

case NOV : cout << “ November ” ; break ;case DEC : cout << “ December ” ; break ;

}

}

19


20

enum SchoolType { PRE_SCHOOL, ELEM_SCHOOL, MIDDLE_SCHOOL, HIGH_SCHOOL, COLLEGE } ;

.

.

.

SchoolType GetSchoolData ( void )

// Obtains information from keyboard to determine school level// Postcondition: Function value == personal school level{

SchoolType schoolLevel ;

int age ;

int lastGrade ;

cout << “Enter age : “ ; // prompt for information

cin >> age ;

Function with enum type Return Value

20


21

if ( age < 6 )

schoolLevel = PRE_SCHOOL ;

else

{ cout << “Enter last grade completed in school : “ ;

cin >> lastGrade;

if ( lastGrade < 5 )

schoolLevel = ELEM_SCHOOL ;

else if ( lastGrade < 8 )

schoolLevel = MIDDLE_SCHOOL ;

else if ( lastGrade < 12 )

schoolLevel = HIGH_SCHOOL ;

else

schoolLevel = COLLEGE ;

}

return schoolLevel ; // return enum type value

}

21


22

Multifile C++ Programs

• C++ programs often consist of several different files with extensions such as .h and .cpp

• related typedef statements, const values, enum type declarations, and similar items are often placed in user-written header files

• by using the #include preprocessor directive the contents of these header files are inserted into any program file that

uses them


23

Inserting Header Files

#include <iostream> // iostream

#include “school.h”

int main ( )

{ enum SchoolType

{ PRE_SCHOOL,

. ELEM_SCHOOL,

. MIDDLE_SCHOOL,

. HIGH_SCHOOL, COLLEGE } ;

}


24

Anonymous Data Types

• Anonymous - a data type in which values are directly specified in the variable declaration with no type name, for example:

enum {basketball, football, baseball} mysport;

• Creating an anonymous type has drawbacks

We cannot pass an anonymous type as a parameter to a function

• use them with care !!!


25

Anonymous Data Types

• A function cannot return a value of an anonymous type

• Values used in one can be used in another, but they are treated differently


26

typedef Statement

• You can create synonyms or aliases to a previously defined data type by using the typedef statement

• The syntax of the typedef statement is:

typedef existingTypeName newTypeName;

• typedef does not create any new data types• typedef creates an alias to an existing data type

typedef creates an additional name for an already existing data type


27

typedef statement

• before bool type became part of ISO-ANSI C++, a Boolean type was simulated this way

typedef int Boolean; // new data type Booleanconst Boolean true = 1 ;const Boolean false = 0 ;

.

.

.

Boolean dataOK ;...

dataOK = true ;


28

ANSI/ISO Standard C++

• ANSI/ISO standard C++ was officially approved in July 1998

• Most of the recent compilers are also compatible with ANSI/ISO standard C++

this book focus

• For the most part, standard C++ and ANSI/ISO standard C++ are the same, but

• ANSI/ISO Standard C++ has some features not available in Standard C++


29

Namespaces

• When a header file, such as iostream, is included in a program• Global identifiers in the header file also become global

identifiers in the program

• If a global identifier in a program has the same name as one of the global identifiers in the header file• The compiler will generate a syntax error (such as

identifier redefined)

• The same problem can occur if a program uses third party libraries


30

Namespaces (continued)

• To overcome this problem, third party vendors begin their global identifiers with a special symbol

• Because compiler vendors begin their global identifier with _ (underscore)• To avoid linking errors, do not begin identifiers

in your program with _

• ANSI/ISO standard C++ attempts to solve this problem of overlapping global identifier names with the namespace mechanism


31

Syntax: namespace• The syntax of the statement namespace is:

namespace namespace_name{

members}

• where a member is usually a variable declaration, a named constant, e.g. const double rate = 7.50; a function, e.g. void printResult(); or another namespace

namespace globalType // e.g.{

const double rate = 7.50;void printResult();

}


32

Accessing a namespace Member

• The scope of a namespace member is local to the namespace

• Usually two ways a namespace member can be accessed outside the namespace

1. One way is to use the syntax:

namespace_name::identifier To access the member rate of the namespace

globalType, the following statement is required:globalType::rate

• To access the function printResult, the following statement is required:

globalType::printResult();


33

Accessing a namespace Member

2. To simplify the accessing of all namespace members:

using namespace namespace_name;

e.g. using namespace globalType;

using namespace std;

3. To simplify the accessing of a specific namespace member:

using namespace_name::identifier;

e.g. using globalType::rate;


34

The using Statement

• After the using statement• Not necessary to precede the namespace_name ::

before the namespace member

• e.g. p.399/4 either x or expN::x

• If a namespace member and a global identifier or a block identifier have the same name• namespace_name :: must precede the

namespace member

• e.g. p.398/2 expN::x


35

The string Type p.1475

• To use the data type string, the program must include the header file <string> p.1475

• The statement:

string name = "William Jacob";

declares name to be a string variable and also initializes name to "William Jacob"

• The first character, 'W', in name is in position 0,

• the second character, 'i', is in position 1, and so on


36

The string Type (continued)

• The variable name is capable of storing any size string

• Binary operator + (to allow the string concatenation operation), and the array subscript operator [ ], have been defined for the data type string

• If str1 = "Sunny", the statement stores the string "Sunny Day" into str2:

str2 = str1 + " Day";


37

length Function

• Length returns the number of characters currently in the string

• The syntax to call the length function is:

strVar.length()where strVar is variable of the type string• no arguments

• length returns an unsigned integer

• The value returned can be stored in an integer variable


38

size Function

• The function size is same as the function length• Both functions return the same value

• The syntax to call the function size is:strVar.size()

where strVar is variable of the type string

• has no arguments


39

find Function

• find searches a string for the first occurrence of a particular substring

• Returns an unsigned integer value of type string::size_type (an unsigned integral (data) type)

giving the result of the search

• The syntax to call the function find is:strVar.find(strExp)

where strVar is a string variable and strExp is a string expression evaluating to a string

• The string expression, strExp, can also be a character


40

find Function (continued)

• If successful, find returns the position in strVar where the match begins

• For the search to be successful the match must be exact

• If unsuccessful, find returns the special value string::npos (“not a position within the string”) – max value of data type string


41

substr Function

• substr returns a particular substring of a string

• The syntax to call the function substr is:

strVar.substr(expr1,expr2)

• where expr1 and expr2 are expressions evaluating to unsigned integers

• The expression expr1 specifies a position within the string (starting position of the substring)

• The expression expr2 specifies the length of the substring to be returned


42

swap Function

• swap interchanges the contents of two string variables

• The syntax to use the function swap is

strVar1.swap(strVar2);where strVar1 and strVar2 are string variables

• Suppose you have the following statements:string str1 = "Warm";

string str2 = "Cold";

• After str1.swap(str2); executes, the value of str1 is "Cold" and the value of str2 is "Warm"


43

Programming Example: Pig Latin Strings p.410

• Program prompts user to input a string

• Then outputs the string in the pig Latin form

• The rules for converting a string into pig Latin form are as follows:

1. If the string begins with a vowel, add the string "-way" at the end of the string

− For example, the pig Latin form of the string "eye" is "eye-way“


44

Pig Latin Strings (continued)

2. If the string does not begin with a vowel, first add "-" at the end of the string

− Then move the 1st of the string to the end of the string until the first character of the string becomes a vowel

− Next, add the string "ay" at the end

− For example, the pig Latin form of the string "There" is "ere-Thay“

− For this program the vowels are a, e, i, o, u, y, A, E, I, O, U, and Y the pig Latin form of "by" is "y-bay“


45

Pig Latin Strings (continued)

3. Strings such as "1234" contain no vowels − The pig Latin form of a string that has no vowels

in it is the string followed by the string "-way“

− For example, the pig Latin form of the string "1234" is "1234-way“


46

Problem Analysis

• If str denotes a string

• Check the first character, str[0], of str

• If str[0] is a vowel, add "-way" at the end of str

• If the first character of str, str[0], is not a vowel

First add "-" at the end of the string

Remove the first character of str from str and put it at end of str

• Now the second character of str becomes the first character of str

• This process is repeated until either

1. The first character of str is a vowel

2. All characters of str are processed, in which case str does not contain any vowels


47

Algorithm Design

• The program contains the following functions:• isVowel - to determine whether a character is

a vowel• rotate - to move first character of str to the end

of str• pigLatinString - to find the pig Latin form of

str• Main Algorithm:

1. Get str2. Use the function pigLatinString to find the pig

Latin form of str 3. Output the pig Latin form of str


48

Function isVowel

bool isVowel(char ch){

switch(ch){case 'A': case 'E': case 'I': case 'O': case 'U': case 'Y':case 'a': case 'e': case 'i': case 'o': case 'u': case 'y': return true;default: return false;}

}


49

Function rotate (continued)

string rotate(string pStr) // Takes a string as a parameter{

int len = pStr.length();string rStr;rStr = pStr.substr(1,len - 1) + pStr[0]; // Removes

1st

// chr and places it at end

return rStr;}


50

// Pig Latin Strings p.410#include <iostream>#include <string>using namespace std;

bool isVowel(char ch);string rotate(string pStr);string pigLatinString(string pStr);

int main(){

string str;

cout << "Enter a string: ";cin >> str;cout << endl;

cout << "The pig Latin form of " << str << " is: " << pigLatinString(str) << endl;

return 0;}

bool isVowel(char ch){

switch (ch){case 'A': case 'E': case 'I': case 'O': case 'U': case 'Y':case 'a': case 'e': case 'i': case 'o': case 'u': case 'y': return true;default: return false;}

}

string rotate(string pStr){

string::size_type len = pStr.length();string rStr;rStr = pStr.substr(1, len - 1) + pStr[0];return rStr;

}string pigLatinString(string pStr) // see next slide{

string::size_type len;bool foundVowel;string::size_type counter;

if (isVowel(pStr[0])) //Step 1 pStr = pStr + "-way";else //Step 2{ pStr = pStr + '-'; pStr = rotate(pStr); //Step 3

len = pStr.length(); //Step 3.a foundVowel = false; //Step 3.b

for (counter = 1; counter < len - 1; counter++)//Step 3.d if (isVowel(pStr[0])) { foundVowel = true; break; } else //Step 3.c pStr = rotate(pStr);

if (!foundVowel) //Step 4 pStr = pStr.substr(1, len) + "-way"; else

pStr = pStr + "ay"; }return pStr; //Step 5}


51

1. If pStr[0] is a vowel, add "-way" at end

of pStr

2. If pStr[0] is not a vowel3a. Move the first character of pStr to the

end of pStr The second character of pStr

becomes the first character of pStr• Now pStr may or may not contain a

vowel

3b. Use a Boolean variable, foundVowel, which is set to true if pStr contains a vowel and false otherwise

initialize foundVowel to false

3c. if pStr[0] is not a vowel, move str[0] to the end of pStr by calling the function rotate

repeat above step until either the first character of pStr becomes a vowel or all characters of pStr have been checked

4. Convert pStr into the pig Latin form

5. Return pStr

string pigLatinString(string pStr){

string::size_type len;bool foundVowel;string::size_type counter;

if (isVowel(pStr[0])) //Step 1 pStr = pStr + "-way";else //Step 2{ pStr = pStr + '-'; pStr = rotate(pStr); //Step 3

len = pStr.length(); //Step 3.a foundVowel = false; //Step 3.b

for (counter = 1; counter < len - 1; counter++) if (isVowel(pStr[0])) { foundVowel = true; break; } else //Step 3.c pStr = rotate(pStr);

if (!foundVowel) //Step 4 pStr = pStr.substr(1, len) + "-way"; else

pStr = pStr + "ay"; }return pStr; //Step 5}


52

Summary

• An enumeration type is a set of ordered values• Reserved word enum creates an enumeration

type

• No arithmetic operations are allowed on the enumeration type

• Relational operators can be used with enum values

• Enumeration type values cannot be input or output directly


53

Summary

• An anonymous type is one where a variable’s values are specified without any type name

• C++’s reserved word typedef creates synonyms or aliases to previously defined data types

• The namespace mechanism is a feature of ANSI/ISO Standard C++

• A namespace member is usually a named constant, variable, function, or another namespace


54

Summary

• The keyword namespace must appear in the using statement

• A string is a sequence of zero or more characters• Strings in C++ are enclosed in double

quotation marks

• In C++, [] is called the array subscript operator

• The function length returns the number of characters currently in the string


55

Summary

• The function size returns the number of characters currently in the string

• The function find searches a string to locate the first occurrence of a particular substring

• The function substr returns a particular substring of a string

• The function swap is used to swap the contents of two string variables

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C++ Programming: Program Design Including Data Structures, Second Edition

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