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:
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:
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:
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.
