Abstract Data TypesAbstract Data Types

Applied Arrays: Lists and Applied Arrays: Lists and StringsStrings

Chapter 12 - 13Chapter 12 - 13

ENUMERATION TypeENUMERATION Type

A data type is a set of values together with a set of operations on those values.

In order 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.

C++ allows the user to define a new simple data type by specifying its name and the values, but not the operations.

The values that we specify for the data type must be identifiers.

The syntax for enumeration type is:

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

where value1, value2, … are identifiers.

value1, value2, … are called enumerators. In C++, enum is a reserved word. Enumeration type is an ordered set of

values.

Example:

enum colors{brown, blue, red, green, yellow};

defines a new data type, called colors

The values belonging to this data type are brown, blue, red, green, and yellow.

Example:

enum standing{freshman, sophomore, junior, senior};

defines standing to be an enumeration type. The values belonging to standing are freshman, sophomore, junior, and senior.

Example:

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

//Illegal enumeration types

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};

If a value has already been used in one enumeration type, it cannot be used by any other enumeration type in the same block.

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

Example:

enum mathStudent{John, Bill, Cindy, Lisa, Ron};enum compStudent{Susan, Cathy, John, William}; //Illegal

Suppose that these statements are in the same program in the same block.

The second enumeration type, compStudent, is not allowed because the value John was used in the previous enumeration type mathStudent.

Declaring VariablesDeclaring Variables

The syntax for declaring variables is the same as before, that 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;

AssignmentAssignment

The statement

popularSport = football;

stores football in popularSport

The statement

mySport = popularSport;

copies the content of popularSport in mySport.

Operations on Enumeration TypesOperations on Enumeration Types

No arithmetic operation is allowed on enumeration type.

The following statements are illegal;

mySport = popularSport + 2; //illegalpopularSport = football + soccer; //illegalpopularSport = popularSport * 2; // illegal

Also, the increment and decrement operations are not allowed on enumeration types.

The following statements are illegal;

popularSport++; //illegalpopularSport--; //illegal

To increment the value of popularSport by 1, we can use the cast operator as follows:

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

Consider the following statements:

popularSport = football;

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

After the second statement, the value of popularSport will be hockey.

The following statements results in storing basketball in popularSport.

popularSport = football;

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

Relational OperatorsRelational Operators

Suppose we have the enumeration type sports and the variables popularSport and mySport as defined above. Then

football <= soccer is truehockey > basketball is truebaseball < football is false

If

popularSport = soccer;

mySport = volleyball;

then

popularSport < mySport is true

Enumeration Types and LoopsEnumeration Types and Loops

Suppose mySport is a variable as declared above.

for(mySport = basketball; mySport <= soccer; mySport = static_cast<sports>(mySport+1))

...

•This for loop executes 5 times.

Input/Output of Enumeration Input/Output of Enumeration TypesTypes

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).

You can input and output enumeration indirectly

Example:enum courses{algebra, basic, pascal, cpp, philosophy, analysis, chemistry, history};

courses registered;

char ch1,ch2;cin>>ch1>>ch2; //read two characters

switch(ch1){case 'a': if(ch2 == 'l') registered = algebra;

else registered = analysis; break;case 'b': registered = basic;

break;

case 'c': if(ch2 == 'h') registered = chemistry;

else registered = cpp;

break;case 'h': registered = history;

break;case 'p': if(ch2 == 'a') registered = pascal;

else registered = philosophy;

break;default: cout<<"Illegal input."<<endl;}

Enumeration type can be output indirectly as follows:

switch(registered){case algebra: cout<<"algebra";

break;case analysis: cout<<"analysis"; break;case basic: cout<<"basic"; break;case chemistry: cout<<"chemistry";

break;case cpp: cout<<"cpp"; break;case history: cout<<"history";

break;case pascal: cout<<"pascal";

break;case philosophy: cout<<"philosophy";}

enum courses{algebra, basic, pascal, cpp, philosophy, analysis, chemistry, history};

courses registered;

If you try to output the value of an enumerator directly, the computer will output the value assigned to the enumerator.

Suppose that registered = algebra; The following statement outputs the value 0

because the (default) value assigned to algebra is 0:

cout<<registered<<endl;

The following statement outputs 4:

cout<<philosophy<<endl;

Functions and Enumeration TypesFunctions 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.

courses readCourses(){ courses registered; char ch1,ch2;

cout<<"Enter the first two letters of the course: "<<endl; cin>>ch1>>ch2;

switch(ch1) { case 'a': if(ch2 == 'l')

registered = algebra; else

registered = analysis; break;

case 'b': registered = basic; break;

case 'c': if(ch2 == 'h') registered = chemistry; else

registered = cpp; break;

case 'h': registered = history; break;

case 'p': if(ch2 == 'a') registered = pascal; else

registered = philosophy; break;

default: cout<<"Illegal input."<<endl; } //end switch

return registered;} //end readCourses

void printEnum(courses registered){ switch(registered) {

case algebra: cout<<"algebra"; break;

case analysis: cout<<"analysis"; break;

case basic: cout<<"basic"; break;

case chemistry: cout<<"chemistry"; break;

case cpp: cout<<"cpp"; break;

case history: cout<<history"; break;

case pascal: cout<<"pascal"; break;

case philosophy: cout<<"philosophy"; } //end switch} //end printEnum

Declaring Variables When Declaring Variables When Defining the Enumeration Defining the Enumeration

Type Type

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

enum coins{penny, nickel, dime, halfDollar,

dollar} change, usCoins;

Anonymous Data TypesAnonymous Data Types

A data type in which values are directly specified in the variable declaration with no type name is called an anonymous type.

enum {basketball, football, baseball, hockey} mysport;

Creating an anonymous type has drawbacks. We cannot pass an anonymous type as a parameter to a

function. A function cannot return a value of an anonymous type. Values used in one anonymous type can be used in another

anonymous type, but variables of those types are treated differently.

enum {English, French, Spanish, German, Russian} languages;enum {English, French, Spanish, German, Russian} foreignLanguages;

languages = foreignLanguages; //illegal

The typedef Statement

In C++, you can create synonyms or aliases to a previously defined data type by using the typedef statement.

The general syntax of the typedef statement is

typedef existingTypeName newTypeName;

In C++, typedef is a reserved word. The typedef statement does not create any new data type; it creates only an alias to an existing data type.

Example:

The following statement creates an alias, integer, for the data type int.

typedef int integer;

The following statement creates an alias, real, for the data type double.

typedef double real;

The following statement creates an alias, decimal, for the data type double.

typedef double decimal;

Example:typedef int Boolean; //Line 1

const Boolean True = 1; //Line 2const Boolean False = 0; //Line 3

Boolean flag; //Line 4

The statement at Line 1 creates an alias, Boolean, for the data type int.

The statements at Lines 2 and 3 declare the named constants True and False and initialize them to 1 and 0, respectively.

The statement at Line 4 declares flag to be a variable of the type Boolean.

Because flag is a variable of the type Boolean, the following statement is legal:

flag = True;

The string TypeThe string Type

• To use the data type string, the program must include the header file string

#include <string>

• The statement

string name = "William Jacob";

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

• The position of the first character, 'W', in name is 0, the position of the second character, 'i', is 1, and so on.

• The variable name is capable of storing (just about) any size string.

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

Suppose we have the following declarations.

string str1, str2, str3;

The statement

str1 = "Hello There";

stores the string "Hello There" in str1. The statement

str2 = str1;

copies the value of str1 into str2.

•If str1 = "Sunny", the statement

str2 = str1 + " Day";

stores the string "Sunny Day" into str2.

• If

str1 = "Hello"

and

str2 = "There".

then

str3 = str1 + " " + str2;

stores "Hello There" into str3.

•This statement is equivalent to the statement

str3 = str1 + ' ' + str2;

•The statement

str1 = str1 + "Mickey";

updates the value of str1 by appending the string "Mickey" to its old value.

•If str1 = "Hello there", the statement

str1[6] = 'T';

replaces the character t with the character T.

• The data type string has a data type, string::size_type, and a named constant, string::npos, associated with it.

string::size_type An unsigned integer (data) type

string::npos The maximum value of the (data) type

string::size_type, a number such as 4294967295 on many machines

The length Function

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

The value returned is an unsigned integer. The syntax to call the length function is:

strVar.length()

where strVar is variable of the type string.

The function length has no arguments.

Consider the following statements:

string firstName;

string name;

string str;

firstName = "Elizabeth";

name = firstName + " Jones";

str = "It is sunny.";

Statement Effectcout<<firstName.length()<<endl; Outputs 9cout<<name.length()<<endl; Outputs 15cout<<str.length()<<endl; outputs 12

•The function length returns an unsigned integer.•The value returned can be stored in an integer

variable. •Since the data type string has the data type string::size_type associated with it, the variable to hold the value returned by the length function is usually of this type.

string::size_type len;

Statement Effect

len = firstName.length(); The value of len is 9

len = name.length(); The value of len is 15

len = str.length(); The value of len is 12

The size Function

The function size is same as the function length. Both these functions return the same value. The syntax to call the function size is:

strVar.size()

where strVar is variable of the type string.

As in the case of the function length, the function size has no arguments.

The find Function

• The find function searches a string to find the first occurrence of a particular substring and returns an unsigned integer value (of type string::size_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.

• If the search is successful, the function find returns the position in strVar where the match begins.

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

• If the search is unsuccessful, the function returns the special value string::npos (“not a position within the string”).

The following are valid calls to the function find.

str1.find(str2) str1.find("the")

str1.find('a')

str1.find(str2+"xyz")

str1.find(str2+'b')

string sentence;string str;string::size_type position;

sentence = "It is cloudy and warm.";

str = "cloudy";

Statement Effect

cout<<sentence.find("is")<<endl; Outputs 3

cout<<sentence.find("and")<<endl; Outputs 13

cout<<sentence.find('s')<<endl; Outputs 4

cout<<sentence.find(str)<<endl; Outputs 6

cout<<sentence.find("the")<<endl; Outputs the value of string::nops

position = sentence.find("warm"); Assigns 17 to position

The substr Function

• The substr function 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.

string sentence;

string str;

sentence = "It is cloudy and warm.";

Statement Effectcout<<sentence.substr(0,5) Outputs: It is

<<endl;

cout<<sentence.substr(6,6) Outputs: cloudy<<endl;

cout<<sentence.substr(6,16) Outputs: cloudy and warm. <<endl;

cout<<sentence.substr(3,6) Outputs: is clo<<endl;

str = sentence.substr(0,8); str = "It is cl"

str = sentence.substr(2,10); str = " is cloudy"

The Function swapThe Function swap

The function swap is used to swap 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 the following statement executes, the value of str1 is "Cold" and the value of str2 is "Warm".

str1.swap(str2);

Function isVowel 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;}

}

Function rotate

This function takes a string as a parameter, removes the first character of the string, and places it at the end of the string.

This is done by extracting the substring starting at position 1 until the end of the string, and then adding the first character of the string.

string rotate(string pStr){int len = pStr.length();

string rStr;

rStr = pStr.substr(1,len - 1) + pStr[0];

return rStr;}

Things about StringsThings about Strings

• Made up of individual characters• Denoted by double quotes• Have invisible character at end

called “null terminator character” (‘\0’)

• How many characters in the word “cat”?

44

String in C++ String in C++

A string is an array of characters which contains a non-printing null character ‘\0’

( with ASCII value 0 ) marking its end.

A string can be initialized in its declaration in two equivalent ways.

char message [ 8 ] = { ‘H’, ‘e’, ‘l’, ‘l’, ‘o’, ‘\0’ };

char message [ 8 ] = “Hello” ;

message [0] [1] [2] [3] [4] [5] [6] [7]

‘H’ ‘e’ ‘l’ ‘l’ ‘o’ ‘\0’

45

charchar vs. string vs. string

‘A’ has data type charand is stored in 1 byte

“A” is a string of 2 charactersand is stored in 2 bytes

5000

‘A’

6000

‘A’

6001

‘\0’

46

Recall that . . .Recall that . . .

char message[8]; // this declaration allocates memory

To the compiler, the value of the identifier message alone is the base address of the array. We say message is a pointer (because its value is an address). It “points” to a memory location.

message [0] [1] [2] [3] [4] [5] [6] [7]

‘H’ ‘e’ ‘l’ ‘l’ ‘o’ ‘\0’

6000

Declaring StringsDeclaring Strings

• Can do multiple ways:char charArray [255]; // set size of array

to 255char *charArray = “blah blah blah”;// sets charArray pointing to space that’s

15 big

• Both ways accomplish the same thing because both are pointers to memory

Reading String from the UserReading String from the User

• Use cin to get a word

char charArray [255];cin >> charArray;

• Use cin.getline ( ) to get entire line of text

cin.getline (charArray, 255);

setw( )setw( )

• There is a danger when getting input

• User can type a string longer than the array you have set up

• This will result in a crash! (trying to go into someone else’s memory)

• Use setw( ) to solve!• Example:

cin >> setw (255) >> charArray;

Ensure input does not exceed size of array

Printing StringsPrinting Strings

• Simple: use cout to do this

• Example:cout << charArray << endl;

String FunctionsString Functions

Whole library dedicated to strings

#include <string.h>

• strcpy (char *, char *) // returns a char *

• strcat (char *, char *) // returns a char *• strcmp (char *, char *) // returns an int• strtok (char *, char *) // returns char *

strcmp ( )strcmp ( )

Used to compare two strings• CANNOT TYPE:

if (string1 == string2)

• Example:int result = strcmp (“Hello”, “World”);

// if result < 0, then “hello” is < “world”// if result == 0, then “hello” has the same

chars// if result > 0, then “hello” > “world” (but

it’s not)

strtok ( )strtok ( )

Token - sequence of chars separated by some delimiter

• Example:When,in,the,course,of,human,events,it,

becomes

• What are tokens?• What is delimiter?

Answer: the words!

Answer: the comma - so we saythis is a comma delimited string of tokens

UsageUsage(Pass NULL for each successive call)(Pass NULL for each successive call)

#include <iostream.h>#include <string.h>void main ( ) {

char charArray [ ] = “Hello to the World”;char *tokenPtr;

tokenPtr = strtok (charArray, “ “);while (tokenPtr !=NULL) {

cout << tokenPtr << endl;tokenPtr = strtok (NULL, “ “);

}}

Notice the NULL!

Output: Hello to the World

More CodeMore Code

void main ( ) {char charArray [ ] = “Hello to the World”;char *tokenPtr;

tokenPtr = strtok (charArray, “e“);while (tokenPtr !=NULL) {

cout << tokenPtr << endl;tokenPtr = strtok (NULL, “e“);

}}

Output: H llo to th World

56

Recall that . . .Recall that . . .

char message[8]; // this declaration allocates memory

To the compiler, the value of the identifier message alone is the base address of the array. We say message is a pointer (because its value is an address). It “points” to a memory location.

message [0] [1] [2] [3] [4] [5] [6] [7]

‘H’ ‘e’ ‘l’ ‘l’ ‘o’ ‘\0’

6000

End of LectureEnd of Lecture

• Next Time, Lists and Lists as Abstract Data Types

• Program #3, Due 10/21 – The Battle Ship Game

58

Aggregate String I/O in C++ Aggregate String I/O in C++

I/O of an entire string is possible using the array identifier with no subscripts and no looping.

EXAMPLE

char message [ 8 ] ; cin >> message ; cout << message ;

59

Extraction operator >>Extraction operator >>

When using the extraction operator ( >> ) to read input characters into a string variable,

• the >> operator skips any leading

white space characters such as blanks and new lines.

• It then reads successive characters into the array, and stops at the first trailing white space character.

• The >> operator adds the null character to the end of the string.

60

Example using >>Example using >>

char name [ 5 ] ;cin >> name ;

Suppose input stream looks like this: J o e

name [0] name [1] name [2] name [3] name [4]

7000

total number of elements in the array

null character is added

‘J’ ‘o’ ‘e’ ‘\0’

61

Function get( )Function get( )

• Because the extraction operator stops reading at the first trailing white space, >> cannot be used to input a string with blanks in it.

• If your string’s declared size is not large enough to hold the input characters and add the ‘\0’, the extraction operator stores characters into memory beyond the end of the array.

• Use get function with 2 parameters to overcome these obstacles.

char message [ 8 ] ;cin.get (message, 8) ; // inputs at most 7 characters plus ‘\0’

62

inFileStream.get ( str, count + inFileStream.get ( str, count + 1)1)

• get does not skip leading white space characters such as blanks and new lines.

• get reads successive characters (including blanks) into the array, and stops when it either has read count characters, or it reaches the new line character ‘\n’, whichever comes first.

• get appends the null character to str.

• If it is reached, new line is not consumed by get, but remains waiting in the input stream.

63

Function ignore( ) Function ignore( )

• can be used to consume any remaining characters up to and including the new line ‘\n’ left in the input stream by get

cin.get ( string1, 81 ) ; // inputs at most 80 characters

cin.ignore ( 30, ‘\n’ ) ; // skips at most 30 characters // but stops if ‘\n’ is read

cin.get ( string2, 81 ) ;

64

Another example using get( )Another example using get( )

char ch ;char fullName [ 31 ] ;char address [ 31 ] ;

cout << “Enter your full name: “ ;cin.get ( fullName, 31 ) ;cin.get (ch) ; // to consume the new

linecout << “Enter your address: “ ;cin.get ( address, 31 ) ;

fullName [0]

‘N’ ‘e’ ‘l’ ‘l’ ‘ ’ ‘D’ ‘a’ ‘l’ ‘e’ ‘\0’ . . .

address [0]

‘A’ ‘u’ ‘s’ ‘t’ ‘i‘ ‘n’ ‘ ’ ‘T’ ‘X’ ‘\0’ . . .

65

String function prototypes inString function prototypes in< string.h >< string.h >

int strlen (char str [ ] ); // FCTNVAL == integer length of string str ( not including ‘\0’ )

int strcmp ( char str1 [ ], char str2 [ ] ); // FCTNVAL == negative, if str1 precedes str2

lexicographically// == positive, if str1 follows str2 lexicographically// == 0, if str1 and str2 characters same through ‘\0’

char * strcpy ( char toStr [ ], char fromStr [ ] );// FCTNVAL == base address of toStr ( usually ignored )// POSTCONDITION : characters in string fromStr are copied to// string toStr, up to and including ‘\0’, // overwriting contents of string toStr

# include <string.h> . . .

char author [ 21 ] ;int length ;

cin.get ( author , 21 ) ;length = strlen ( author ) ; // What is the value of length ?

5000

author [0]

‘C’ ‘h’ ‘i’ ‘p’ ‘ ’ ‘W’ ‘e’ ‘e’ ‘m’ ‘s’ ‘\0’ . . . .

char myName [ 21 ] = “Huang” ; // WHAT IS OUTPUT?char yourName [ 21 ] ;

cout << “Enter your last name : “ ;cin.get ( yourName, 21 ) ;

if ( strcmp ( myName, yourName ) == 0 )cout << “We have the same name! “ ;

else if ( strcmp ( myName, yourName ) < 0 )cout << myName << “ comes before “ << yourName ;

else if ( strcmp ( myName, yourName ) > 0 )cout << yourName << “comes before “ << myName ;

myName [0]

‘H’ ‘u’ ‘a’ ‘n’ ‘g’ ‘\0’ . . .

yourName [0]

‘H’ ‘e’ ‘a’ ‘d’ ‘i‘ ‘n’ ‘ g’ ‘t’ ‘o’ ‘n’ ‘\0’ . . .

char myName [ 21 ] = “Huang” ;char yourName [ 21 ] ;

if ( myName == yourName ) // compares addresses only!{ // That is, 4000 and 6000 here. . // DOES NOT COMPARE CONTENTS! . .

}

myName [0]

‘H’ ‘u’ ‘a’ ‘n’ ‘g’ ‘\0’ . . .

yourName [0]

‘H’ ‘e’ ‘a’ ‘d’ ‘i‘ ‘n’ ‘ g’ ‘t’ ‘o’ ‘n’ ‘\0’ . . .

4000

6000

char myName [ 21 ] = “Huang” ;char yourName [ 21 ] ;

cin.get ( yourName, 21 ) ;yourName = myName; // DOES NOT

COMPILE!// What is the value of

myName ?

myName [0]

‘H’ ‘u’ ‘a’ ‘n’ ‘g’ ‘\0’ . . .

yourName [0]

4000

6000

‘H’ ‘e’ ‘a’ ‘d’ ‘i‘ ‘n’ ‘ g’ ‘t’ ‘o’ ‘n’ ‘\0’ . . .

char myName [ 21 ] = “Huang” ;char yourName [ 21 ] ;

cin.get ( yourName, 21 ) ;strcpy ( yourName, myName ) ; // changes string yourName

// OVERWRITES CONTENTS!

myName [0]

‘H’ ‘u’ ‘a’ ‘n’ ‘g’ ‘\0’ . . .

yourName [0]

‘H’ ‘e’ ‘a’ ‘d’ ‘i‘ ‘n’ ‘ g’ ‘t’ ‘o’ ‘n’ ‘\0’ . . .

4000

6000 ‘u’ ‘n’ ‘g’ ‘\0’

71

Using Using typedef typedef with arrays with arrays

typedef int Boolean ; // names Boolean as a data type

typedef char String20 [ 21 ] ; // names String20 as an array type

String20 myName ; // these declarationsString20 yourName ; // allocate memory for 3 variablesBoolean isSeniorCitizen ;

5000

7000

6000

72

Write a program that will...Write a program that will...

Read the ID numbers, hourly wages, and names, for up to 50 persons from a data file.

Then display the ID number and hourly wage for any person in the file whose name is entered at the keyboard, or indicate that the person was not located, if that is the case.

73

Assume file has this form with data Assume file has this form with data for no more than 50 personsfor no more than 50 persons

4562 19.68 Dale Nell 1235 15.75 Weems Chip 6278 12.71 Headington Mark . . . . . . . . .

8754 17.96 Cooper Sonia2460 14.97 Huang Jeff

74

Parallel arrays hold related dataParallel arrays hold related data

const int MAX_PERSONS = 50;

typedef char String20[ 21] ; // define data type . . .

// declare 3 parallel arraysint idNums[ MAX_PERSONS ] ; float wages[ MAX_PERSONS ] ; String20 names[ MAX_PERSONS ] ;

// holds up to 50 strings each with// up to 20 characters plus null character ‘\0’

75

idNums[ 0 ] 4562 wages[ 0 ] 19.68 names[ 0 ] “Dale Nell”

idNums[ 1 ] 1235 wages[ 1 ] 15.75 names[ 1 ] “Weems Chip”

idNums[ 2 ] 6278 wages[ 2 ] 12.71 names[ 2 ] “Headington Mark”

. . . . . . . . . . . . . . . . . .

idNums[ 48] 8754 wages[ 48] 17.96 names[ 48] “Cooper Sonia”

idNums[ 49] 2460 wages[ 49] 14.97 names[ 49] “Huang Jeff”

int idNums [ MAX_PERSONS ] ; int idNums [ MAX_PERSONS ] ; // parallel arrays// parallel arrays

float wages [ MAX_PERSONS ] ; float wages [ MAX_PERSONS ] ;

String20 names [ MAX_PERSONS ] ;String20 names [ MAX_PERSONS ] ;

76

#include < iomanip.h >#include < iostream.h >#include < fstream.h >#include < ctype.h >#include < string.h >#include “bool.h”

typedef char String20 [ 21 ] ;const int MAX_PERSONS = 50 ;

void GetData ( int [ ], float [ ], String20 [ ], int & ) ; // prototypes

void HandleRequests ( int [ ], float [ ], String20 [ ], int ) ;

void LookUp ( String20 [ ], String20, int, Boolean & , int & ) ;

Using array of stringsUsing array of strings

77

Main ProgramMain Program

int main (void){ int idNums [MAX_PERSONS] ; // holds up to 50 IDs float wages [MAX_PERSONS] ; // holds up to 50 wages String20 names [MAX_PERSONS] ; // holds up to 50 names int numPersons; // number of persons’ information in file

GetData ( idNums, wages, names, numPersons ) ;

HandleRequests ( idNums, wages, names, numPersons ) ;

cout << “End of Program.\n”;

return 0 ;}

78

Module Structure Chart

Main

GetData

LookUp

HandleRequests

names oneNamenumPersons

idNums wages names numPersons

idNums wages names numPersons

foundindex

void GetData ( /* out */ int ids[ ] , /* out*/ float wages[ ] , /* out */ String20 names[ ] , /* out */ int &

howMany )

{ ifstream myInfile ; // Reads data from data fileint k = 0 ;

char ch ;

myInfile.open (“A:\\my.dat”) ; if ( ! myInfile ) { cout << “File opening error. Program terminated! “ << endl ; exit ( 1 ) ; } myInfile >> ids[ k ] >> wages [k] ; // get information for first

person myInfile.get(ch) ; // read blank myInfile.get (names[ k ] , 21) ; myInfile.ignore(30, ‘\n’) ; // consume newline

while (myInfile) // while the last read was successful { k++ ;

myInfile >> ids[ k ] >> wages [k] ; myInfile.get(ch) ; // read blank myInfile.get (names[ k ] , 21) ;

myInfile.ignore(30, ‘\n’) ; // consume newline } howMany = k;}

void HandleRequests( const /* in */ int idNums[ ], const /* in */ float wages[ ] , const /* in */ String20 names[ ], /* in */ int numPersons )

{ String20 oneName ; // string to hold name of one person int index ; // will hold an array index value char response; // user’s response whether to continue Boolean found; // has oneName been located in array names

do { cout << “Enter name of person to find: ” ; cin.get (oneName, 21) ;

cin.ignore (100, ‘\n’); // consume newline

LookUp (names, oneName, numPersons, found, index );

if ( found ) cout << oneName << “ has ID # “ << idNums [index]

<< “ and hourly wage $ “ << wages [index] << endl;else cout << oneName << “ was not located. “ << endl;

cout << “Want to find another (Y/N)? “;cin >> response ;response = toupper ( response );

} while ( response == ‘Y’ );}

void LookUp ( const /* in */ String20 names [ ], const /* in */ String20 oneName, /* in */ int numPersons, /* out */ Boolean & found , /* out */ int &

index)

// Sequential search of unordered array. // POSTCONDITION:// IF oneName is in names array// found == true && names[index] == oneName// ELSE// found == false && index == numPersons{

index = 0; found = false; // initialize flag while ( ( ! found ) && ( index < numPersons ) ) // more to

search {

if ( strcmp ( oneName, names[index] ) == 0 ) // match here

found = true ; // change flagelse

index ++ ; }

}

82

Ways to improve efficiency of Ways to improve efficiency of searching processsearching process

• If the array names were sorted, the sequential search for oneName could be aborted as soon as a single name with greater lexicographic (dictionary) order is examined.

• If the array names were sorted, a faster type of search, called a binary search, could be used instead of the slower sequential search.

83

SortingSorting

• means arranging the list elements into some order (for instance, strings into alphabetical order, or numbers into ascending or descending order).

sorting

Dale NellWeems ChipHeadington MarkCooper SoniaHuang Jeff

Cooper Sonia Dale NellHeadington MarkHuang Jeff Weems Chip

84

Selection Sort ProcessSelection Sort Process

• examines the entire list to select the smallest element. Then places that element where it belongs (with array subscript 0).

• examines the remaining list to select the smallest element from it. Then places that element where it belongs (with array subscript 1).

. . .

• examines the last 2 remaining list elements to select the smallest one. Then places that element where it belongs in the array.

85

Selection Sort AlgorithmSelection Sort Algorithm

FOR pass going from 0 through length - 2 Find minimum value in list [ pass . . length-1 ] Swap minimum value with list [ pass ]

length = 5

names [ 0 ] Dale Nell Cooper Sonia names [ 1 ] Weems Chip Weems Chip names [ 2 ] Headington Mark Headington Mark names [ 3 ] Cooper Sonia Dale Nell names [ 4 ] Huang Jeff Huang Jeff

pass = 0

void SelSort ( /* inout */ String20 names [ ] , /* in */ int length )

// Selection sorts names into alphabetic order// Preconditions: length <= MAX_PERSONS// && names [0 . . length -1 ] are assigned// Postcondition: names [ 0 . . length -1 ] are rearranged into order

{ int pass; int place; int minIndex; String20 temp; for ( pass = 0 ; pass < length - 1 ; pass++ )

{ minIndex = pass; for ( place = pass + 1 ; place < length ; place ++ ) if ( strcmp ( names [ place ] , names [ minIndex ] ) < 0 )

minIndex = place; //swap names[pass] with names[minIndex]

strcpy ( temp , names [ minIndex ] ) ; strcpy ( names [ minIndex ] , names [ pass] ) ; strcpy ( names [ pass ] , temp ) ; }}

87

Binary Search in an Binary Search in an Ordered ListOrdered List

• Examines the element in the middle of the array. Is it the sought item? If so, stop searching. Is the middle element too small? Then start looking in second half of array. Is the middle element too large? Then begin looking in first half of the array.

• Repeat the process in the half of the list that should be examined next.

• Stop when item is found, or when there is nowhere else to look and it has not been located.

88

void BinSearch( /* in */ const ItemType list [ ] , /* in */ ItemType item, /* in */ int length, /* out */ int& index,

/* out */ Boolean & found )

// Searches list for item, returning index of item if found

// Precondition:// list [0 . . length - 1 ] are in ascending order // && length is assigned && item is assigned//// Postcondition:// IF item is in list// found == true && list[index] == item// ELSE// found == false && index is undefined

Heading for BinSeach Heading for BinSeach functionfunction

89

{ int first = 0 ; // lower bound on list int last = length - 1 ; // upper bound on list int middle ; // middle index

found = false ; while ( ( last >= first ) && (! found ) )

{ middle = ( first + last ) / 2 ;

if ( item < list [ middle ] )last = middle - 1 ; // look in first half next

else if ( item > list [ middle ] )first = middle + 1; // look in second half next

else found = true ; } index = middle ; }

Body for BinSearch Body for BinSearch functionfunction

90

Trace of BinSearch Trace of BinSearch functionfunction

list[0] [1] [2] [3] [4] [5] [6] [7] [8] [9]

15 26 38 57 62 78 84 91 108 119

item = 45

first middle last

list[0] [1] [2] [3] [4] [5] [6] [7] [8] [9]

15 26 38 57 62 78 84 91 108 119

first middle last

item < list [ middle ] last = middle - 1

item > list [ middle ] first = middle + 1

91

Trace continuedTrace continued

list[0] [1] [2] [3] [4] [5] [6] [7] [8] [9]

15 26 38 57 62 78 84 91 108 119

item = 45

first, middle, last

list[0] [1] [2] [3] [4] [5] [6] [7] [8] [9]

15 26 38 57 62 78 84 91 108 119

first, last middle

item > list [ middle ] first = middle + 1

item < list [ middle ] last = middle - 1

92

Trace concludesTrace concludes

list[0] [1] [2] [3] [4] [5] [6] [7] [8] [9]

15 26 38 57 62 78 84 91 108 119

item = 45

last first

last < first found = false

End of LectureEnd of Lecture