How to use Strings in C++

In this tutorial you will learn what is string, how to use strings in c++, c++ strings, strings in c++ with program examples.

C++ Strings

• It is a set of characters (group of characters) arranged in sequential memory location
• In c/c++, there is no specific built-in data type point to string type 
• We can perform various operations on strings such as
  • Comparing
  • Joining
  • Reversing
  • Indexing and many more, etc,… 
• C++ supports two types of strings. They are
  • C Style String (Character Array)
  • String Class.

1. C STYLE STRING

• In c style string, the string is group of characters terminated with null character
• It will be created either character array or character pointer

Example 1 – String Declaration

     char name[50];

Example 2 – String Definition

     char name[]=”Hello”;

• Here, the array name will hold the values “Hello” with additional null character \0 which is automatically added by the compiler (unlike c)

Memory Representation

I. EXAMPLE OF C STYLE STRING

1. SOURCE CODE

2. OUTPUT

DIFFERENCE BETWEEN C STRING AND STRING CLASS IN C++

S.N	C STRINGS	STRING CLASS
1.	It is statically allocated	It is dynamically allocated
2.	It can be created using character array	It can be created using the predefined class string
3.	Access speed is fast	Access speed is slow
4.	Syntax:string variable-name;	Syntax:  char variable-name[size];
5.	Example:char a[100];	Example:string obj;

2. STRING CLASS

• Here string is created from the predefined type std:string class
• It is available in std global namespace
• It is similar to c strings, while the memory definition, allocation and addition of null character at the end are handled by the string class itself
• Unlike c style string, this type of the string is an object type and it will be allocated dynamically.

BUILT-IN INSTANCE FUNCTIONS OF STRING CLASS

1. append()

• This method is used to append the contents of one string into another string (additionally you can use + operator to append the strings)
• Return type: string

2. push_back(char ch)

• This method is used to add a character at the end of string
• This method will take only one argument which is the character type
• Return type: void

3. push_back()

• This method is used to remove a character at the end of string
• This method does not take any arguments
• Return type: void

4. length()

• This method is used to display the length of the string which is the integer value
• This method does not take any arguments
• Return type: int

5. copy(char [], int length, int pos)

• This method is used to copy the contents of one string into another string
• This method takes three arguments, 
• Where,
  • 1st argument is the name of the target string which is character array
  • 2nd argument is the length which is total number of characters to be copied
  • 3rd argument is the starting position of string which is the integer value
• Return type: int (number of characters to be copied)

6. size()

• This method is used to display the total of length of string in terms of bytes
• It does not take any argument
• Return type: int

7. swap(string)

• This method is used to swap the contents one string with another string
• This method takes only one argument which is the type of string class
• Return type: void

8. compare(string)

• This method is used to compare the two strings and return the integer value
• If the returned value is 0 then both strings are equal else it will be not equal.
• This method takes only one argument which is the string type.
• Return type: int

9. clear()

• This method is used to completely remove all the characters from the string object
• It does not any arguments
• Return type: void

ITERATOR FUNCTIONS

1. begin()

• It is an instance method of string class
• It is used to return the starting point / address of the string
• Return type: iterator

2. end()

• It is an instance method of string class
• It is used to return the ending address of the string which is always point to the null character
• Return type: iterator

OPERATORS USED IN STRING CLASS

• The following operators can be used for the string operations like comparison, appending, lowest, biggest, etc,…

S.N	OPERATORS	USAGE
1.	+	This is used for appending the strings
2.	==	This is used for comparing the two strings
3.	=	This is used for assigning the value to the string
4.	>	This is used to find the biggest string
5.	<	This is used to find the smallest string
6.	[ ]	This is used to access the particular character or sequence of characters in the string
7.	!=	This is used to check whether the two strings are not equal
8.	<<	Displaying Output
9.	>>	Getting Input

I. EXAMPLE OF STRING CLASS

SOURCE CODE

OUTPUT

Drawbacks of cin

• cin object reads a single word at a time. It is not possible to read multiple words at a time
• In order to read lines of text or multiple words, the special method getline() will be used with cin object.

II. READING LINE OF TEXT

SOURCE CODE

 OUTPUT

III. EXAMPLE OF STRING APPEND

SOURCE CODE

#include <iostream>

#include<cstring>

using namespace std;

int main()

{

string y1,y2;

     cout<<“———————————–\n”;

cout<<“\t String Append\n”;

     cout<<“———————————–\n”;

cout<<“Enter the message 1: “;

     getline(cin,y1);

cout<<“Enter the message 2: “;

getline(cin,y2);

// append string c2 to string c1

y1.append(” “+y2);

cout<<“Contents After Appending: \n”;

cout<<y1<<“\n”;

}

OUTPUT

IV. ADDING AND REMOVING CHARACTERS AT END OF THE STRING

1. SOURCE CODE

#include <iostream>

#include<cstring>

using namespace std;

int main()

{

cout<<“——————————————\n”;

cout<<“\t Adding & Removing Characters in String\n”;

     cout<<“——————————————\n”;

string str=”welcome”;

cout<<“Initial String: “<<str<<“\n”;

// add characters one by one et end of the string

str.push_back(‘ ‘);

str.push_back(‘t’);

str.push_back(‘o’);

str.push_back(‘ ‘);

str.push_back(‘c’);

str.push_back(‘h’);

str.push_back(‘e’);

str.push_back(‘n’);

str.push_back(‘n’);

str.push_back(‘a’);

str.push_back(‘i’);

// print after adding characters

cout<<“\nContents after adding characters: \n”;

cout<<“——————————————\n”;

cout<<str<<“\n\n”;

// remove characters at the end of string

str.pop_back();

str.pop_back();

str.pop_back();

str.pop_back();

str.pop_back();

str.pop_back();

str.pop_back();

cout<<“Contents after removing characters: \n”;

cout<<“——————————————\n”;

    cout<<str<<“\n”;

}

OUTPUT

V. EXAMPLE OF SWAPPING OF STRINGS

SOURCE CODE

#include <iostream>

#include<cstring>

using namespace std;

int main()

{

     cout<<“———————————–\n”;

cout<<“\t Swapping Strings\n”;

     cout<<“———————————–\n”;

string d1=”Hello World”;

string d2=”Welcome to Chennai”;

cout<<“Before swapping, Contents: \n”;

cout<<“Text 1: “<<d1<<“\n”;

cout<<“Text 2: “<<d2<<“\n”;

// swap the contents using buiilt-in string swap() function

d1.swap(d2);

cout<<“\nAfter Swapping, Contents: \n”;

     cout<<“———————————–\n”;

cout<<“Text 1: “<<d1<<“\n”;

cout<<“Text 2: “<<d2<<“\n”;

}

OUTPUT

VI. EXAMPLE OF STRING COPYING

SOURCE CODE

#include <iostream>

#include<cstring>

using namespace std;

int main()

{

string inp;

char tar[100];

     cout<<“———————————–\n”;

cout<<“\t C++ String Copy\n”;

     cout<<“———————————–\n”;

cout<<“Enter the string: “;

getline(cin,inp);

// copy the string into another c string using copy() method

inp.copy(tar,inp.length(),0);

cout<<“\nAfter Copying, Contents of C String: \n”;

     cout<<tar<<“\n”;

}

OUTPUT

VII. STRINGS COMPARISON

SOURCE CODE

#include <iostream>

#include<cstring>

using namespace std;

int main()

{

     cout<<“—————————————————\n”;

cout<<“\t String Comparison\n”;

     cout<<“—————————————————\n”;

string w1=”Good Morning”;

string w2=”Good Morning”;

cout<<“String 1: “<<w1<<“\n”;

cout<<“String 2: “<<w2<<“\n”;

// compare the string objects using compare() function

int k=w1.compare(w2);

if(k==0)

{

     cout<<“Both Strings are Equal\n”;

}

else

{

     cout<<“Both Strings are Not Equal\n”;

}

return 42;

} 

OUTPUT

DIFFERENT TYPES OF RETRIEVAL OF STRINGS

• C++ provides several options to retrieve / display the characters of string.

1. Using indexing operator []

2. Using at(int index)

3. Using the Iterator function.

1. Using Indexing

• Here, string can be retrieved using indexing position
• The position can be a positive number.
• Through indexing, the sequence of characters can be displayed.

I.  DISPLAYING STRING USING INDEXING

SOURCE CODE

#include <iostream>

#include<cstring>

using namespace std;

int main()

{

     cout<<“—————————————————\n”;

cout<<“\t Displaying String via Indexing\n”;

     cout<<“—————————————————\n”;

string str=”Good Morning”;

// display the strings using indexing operator []

for(int i=0;i<str.length();i++)

{

     cout<<str[i];

}

cout<<“\n”;

}

OUTPUT

2. Using at(pos) method

• Here, string can be retrieved using the special method named at(int pos)
• The position can be a positive number.
• Like indexing, the sequence of characters can be displayed using this built-in function.

II. DISPLAYING STRING USING at(int) FUNCTION

SOURCE CODE

#include <iostream>

#include<cstring>

using namespace std;

int main()

{

     cout<<“—————————————————\n”;

cout<<“\t Displaying String via at(int)\n”;

     cout<<“—————————————————\n”;

string str=”Welcome to Chennai”;

// display the strings using at(int pos) function

for(int i=0;i<str.length();i++)

{

     cout<<str.at(i);

}

cout<<“\n”;

}

OUTPUT

1. Using Iterator

• Here, string can be retrieved using iterator object
• First, get the starting address of the target input string using the built-in string instance function named string.begin(). This method will return the first address or base address of the input string.
• Once the base address is obtained, then a sequence of characters can be displayed through an iterator object which is like pointer style.

III. DISPLAYING STRING VIA ITERATOR

SOURCE CODE

#include <iostream>

#include<cstring>

using namespace std;

int main()

{

     cout<<“—————————————————\n”;

cout<<“\t Displaying Strings via Iterator\n”;

     cout<<“—————————————————\n”;

string msg=”Welcome to Linux”;

// iterator declaration

string::iterator ir;

// get the base address of string using begin() method

for(ir=msg.begin();*ir!=’\0′;ir++)

{

     cout<<*ir;

}

cout<<“\n”;

return 42;

}

OUTPUT