CSCI 110 STRUCTURED PROGRAMMING WITH C++rafea/CSCE110/Slides/8. Strings.pdf · Prof. amr Goneid, AUC 3 Characters & Strings Characters & their Operations The String Class: String

Prof. amr Goneid, AUC 1

CSCE 110PROGRAMMING FUNDAMENTALS

WITH C++

Prof. Amr GoneidAUC

Part 8. Characters & Strings


Characters & Strings


Characters & Strings Characters & their Operations The String Class: String Objects Declaration Input and Output Member Functions: Length & Indexing Copying , Concatenation & Comparison Other Member Functions Passing String Objects Arrays of Strings Conversions


1. Characters & their Operations Characters: e.g. ‘A’ Character Constants & Variables:

e.g. const char qmark = ‘?’ ;char c;

I/O : e.g. cin >> c; cout << c; Comparison: e.g. (c >= ‘A’) && (c <= ‘Z’) Character Arrays: e.g. char a[20]; Type casting: e.g. int(‘A’) char(65)


Some Character Manipulation Functions Conversion (to) Functions: toupper & tolower

e.g. char a , b ;b = toupper(a);

is Functions: return true or falseisalpha (A – Z , a – z)isdigit (0 – 9)isalnum (A – Z, a – z , 0 – 9)islower (a – z)isupper (A – Z)


2. The String Class: String Objects String Class: Now part of standard library Use #include <string> Strings are “objects” of this class, Member functions

can be used Useful Link:www.cs.utexas.edu/~jbsartor/cs105/CS105_spr10_lec2.pptx.pdf

S t r i n g s a r e O b j e c t s

character

0 1 2

length-1

http://www.cs.utexas.edu/%7Ejbsartor/cs105/CS105_spr10_lec2.pptx.pdf


3. Declaration

String Literals:“Hello”

Constant strings:const string greeting = “Hello ”;

String Objects:string firstName, lastName;string wholeName;string greeting = “Hello “;


C-Style Strings C language has no predefined string data type. It uses character arrays to store strings but appends a

null character ‘\0’ at the end of the string.

e.g. char bird[ ] = “Eagle”; Some C-Style functions are used on C++ strings after

converting them to C-style

E a g l e \00 1 2


Converting to C-Style Strings Example: to convert a character array containing digits

into its integer value. int atoi(const char s[])

Use the c_str member function to convert a string into a character array.

Example: string year = “2015"; int y = atoi(year.c_str());


4. Input & Output

Use extraction operator >> and the stream cin for input ( stops at a blank)cin >> firstName;

Use insertion operator << and the stream cout for outputcout << greeting << wholeName <<

endl;


Input & Output

getline (cin, wholeName, term);reads all characters typed in from the keyboard (including blanks) up to the character stored in term.Such character will not be added to the string.getline (cin, wholename);

will assume the default termination character (end of line or ‘\n’)


5. Member Functions:Length & Indexing Dot notation used to call an objects member

functionswholeName.length();wholeName.at(i) Applies member function length and at to string

object wholeName 1st Function returns the objects length 2nd Function returns character at location [i] in

string object ( equivalent to wholeName [i] )


6. Copying , Concatenation & Comparison Stores the first and last namewholeName = firstName + “ “ + lastName; Concatenation

+ joins the two objects together “ “ for string values not ‘ ‘ Compare two strings using == < > <= >= !=

if ( myName == wholeName ) …….


Example

Build Inverse String:string aword , invword;cin >> aword;invword = “”; // Null Stringfor (i = aword.length()-1; i >= 0; i--)

invword += aword.at(i);cout << invword;


StringOperations.cpp// FILE: StringOperations.cpp// ILLUSTRATES STRING OPERATIONS#include <iostream>#include <string>using namespace std;

int main (){

string firstName, lastName; string wholeName; string greeting = "Hello ";

cout << "Enter your first name: "; cin >> firstName;


StringOperations.cpp

cout << "Enter your last name: "; cin >> lastName;

// Join names in whole name wholeName = firstName + " " + lastName;

// Display results cout << greeting << wholeName <<'!' << endl; cout << "You have " <<

(wholeName.length () - 1) <<" letters in your name." << endl;



// Display initials cout << "Your initials are " <<

(firstName.at(0)) <<(lastName.at(0)) << endl;

return 0;}



Program outputEnter your first name: CarynEnter your last name: Jackson

Hello Caryn Jackson!You have 12 letters in your name.Your initials are CJ


7. Other Member Functions:

.find .append

.insert .swap

.replace .c_str

.erase

.assign

.substr

.empty


.find

message.find(c) or message.find(sub)returns position of character (c) or start ofsubstring (sub) in message. If (c) or (sub) do not exist in message, function returns a long integer > message.length().e.g.message = “one two three”;message.find(‘e’) returns 2message.find(“two”) returns 4


.insert

message.insert( s , newstring)returns message after inserting newstringstarting at location (s)e.g.message = “abcd”; s1 = “klm”; message.insert(2 , s1);changes message to be“abklmcd”


.replace

message.replace(s , n , newstring)returns message after replacing (n)characters by newstring starting at location (s) e.g.message = “during last week”;message.replace(12 , 4 , “month”)changes message to “during last month”


Example

Search and replace:p = message.find(sub);if ((p >= 0) && (p < message.length()))

message.replace(p,sub.length() , news);elsecout << sub << “ not found” << endl;


.erase

message.erase(s , n)returns message after deleting n characters starting at location (s) e.g.message = “one two three”;message.erase(3 , 4)changes message to “one three”


.assign

message.assign(olds , s , n)starting at location (s) in olds, assign tomessage the next n characters.e.g.olds = “abcdef”;message.assign(olds , 2 , 3)changes message to “cde”


.substr

message.substr( s , n)return the substring consisting of (n) characters starting at location (s) inmessagee.g.message = “Good Morning”;cout << message.substr(0 , 2);outputs “Go”


.empty()

message.empty()returns true if message is an emptystring, false otherwisee.g.if (message.empty()) ……….


.append(str)

s.append(s1)returns s after appending s1 at its ende.g.if s = “Last”; s.append(“ Month”);changes s to be “Last Month”


.swap(str)

s.swap(s1)swaps contents of s and s1e.g.if s = “First”; s1 = “Second”;s.swap(s1);changes s to be “Second” and s1 to be“First”


.c_str() s.c_str( )

will return a constant character array having the contents of s and terminated by a null character ‘\0’, i.e. a C_style stringe.g.const char *cstr;cstr = cppstr.c_str();


8. Passing String Objects

String objects are passed like ordinary variables, i.e., either by value or by reference.

If the string is input only, pass by value, e.g. void doit (string s)

If the string is Output or Inout, pass by reference, e.g. void doit (string& s)


Examplevoid moneyToNumberString (string& moneyString){

// Local data . . .int posComma; // position of next comma

// Remove $ from moneyStringif (moneyString.at(0) == '$')

moneyString.erase(0, 1); else if (moneyString.find("-$") == 0)

moneyString.erase(1, 1);


Example (cont)// Remove all commas

posComma = moneyString.find(",");while (posComma >= 0 && posComma <

moneyString.length()){

moneyString.erase(posComma, 1); posComma = moneyString.find(",");

}} // end moneyToNumberString


9. Arrays of Strings

Strings can be elements of arrays.string names[100];declares an array of 100 strings.

names[i] refers to string [i] in the array. names[i].at(j) refers to character (j) of

string [i]. names[i] [j] the same as above


10. Conversions

A c_string of digits can be converted into a number using one of the following functions:

Atoi(c_string) returns type intAtol(c_string) returns type longAtof(c_string) returns type double


Conversion Example#include <string>#include <iostream>#include <stdlib.h>using namespace std;

int main (){

string digits; const char *s; int num;cout << "Enter string of digits : "; cin >> digits;s = digits.c_str();num = atoi(s); cout << num << " " << 2*num << endl;return 0;

}

Documents

CSCI 110 STRUCTURED PROGRAMMING WITH C++rafea/CSCE110/Slides/8. Strings.pdf · Prof. amr Goneid, AUC 3 Characters & Strings Characters & their Operations The String Class: String