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C++ Strings


C++ Strings

Strings are used for storing text.

A string variable contains a collection of characters surrounded by double quotes:

Example

Create a variable of type string and assign it a value:

string greeting = "Hello";

To use strings, you must include an additional header file in the source code, the <string> library:

Example

// Include the string library
#include <string>

// Create a string variable
string greeting = "Hello";
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String Concatenation

The + operator can be used between strings to add them together to make a new string. This is called concatenation:

Example

string firstName = "John ";
string lastName = "Doe";
string fullName = firstName + lastName;
cout << fullName;
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Note that we added a space after firstName to create a space between John and Doe on output.


String Length

A string in C++ is actually an object, which contain functions that can perform certain operations on strings. For example, the length of a string can be found with the length() function:

Example

string txt = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
cout << "The length of the txt string is: " << txt.length();
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Access Strings

You can access the characters in a string by referring to its index number inside square brackets [].

This example prints the first character in myString:

Example

string myString = "Hello";
cout << myString[0];
// Outputs H
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Note: String indexes start with 0: [0] is the first character. [1] is the second character, etc.

This example prints the second character in myString:

Example

string myString = "Hello";
cout << myString[1];
// Outputs e
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Change String Characters

To change the value of a specific character in a string, refer to the index number, and use single quotes:

Example

string myString = "Hello";
myString[0] = 'J';
cout << myString;
// Outputs Jello instead of Hello
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User Input Strings

It is possible to use the extraction operator >> on cin to display a string entered by a user:

Example

string firstName;
cout << "Type your first name: ";
cin >> firstName; // get user input from the keyboard
cout << "Your name is: " << firstName;

// Type your first name: John
// Your name is: John

However, cin considers a space (whitespace, tabs, etc) as a terminating character, which means that it can only display a single word (even if you type many words):

Example

string fullName;
cout << "Type your full name: ";
cin >> fullName;
cout << "Your name is: " << fullName;

// Type your full name: John Doe
// Your name is: John

From the example above, you would expect the program to print "John Doe", but it only prints "John".

That's why, when working with strings, we often use the getline() function to read a line of text. It takes cin as the first parameter, and the string variable as second:

Example

string fullName;
cout << "Type your full name: ";
getline (cin, fullName);
cout << "Your name is: " << fullName;

// Type your full name: John Doe
// Your name is: John Doe
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Adding Numbers and Strings

WARNING!

C++ uses the + operator for both addition and concatenation.

Numbers are added. Strings are concatenated.

If you add two numbers, the result will be a number:

Example

int x = 10;
int y = 20;
int z = x + y;      // z will be 30 (an integer)
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If you add two strings, the result will be a string concatenation:

Example

string x = "10";
string y = "20";
string z = x + y;   // z will be 1020 (a string)
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If you try to add a number to a string, an error occurs:

Example

string x = "10";
int y = 20;
string z = x + y;

Omitting Namespace

You might see some C++ programs that runs without the standard namespace library. The using namespace std line can be omitted and replaced with the std keyword, followed by the :: operator for string (and cout) objects:

Example

#include <iostream>
#include <string>

int main() {
  std::string greeting = "Hello";
  std::cout << greeting;
  return 0;
}
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It is up to you if you want to include the standard namespace library or not.