When we declare a string like this:

string str = "pizza";

what we have behind-the-scenes is an array like this:

Declaring a string actually gives us an array of char variables. We can access the string as a whole by using the string variable's name (str), or access one char at a time by treating str like an array.

We can access each letter of the string directly with the subscript operator, just like an array:

Example: Outputting each letter of a string

cout << str[0] << endl; // Outputs p
cout << str[1] << endl; // Outputs i
cout << str[2] << endl; // Outputs z
cout << str[3] << endl; // Outputs z
cout << str[4] << endl; // Outputs a

Because we can act on a string like an array, this means we can also use a variable to access an arbitrary index of a character in the array…

Example: Accessing one letter at some position i

int i;
cout << "Get which letter? ";
cin >> i;
cout << str[i];

Or even iterate over the string with a for loop…

Example: Iterating and displaying each letter of a string

for ( int i = 0; i < str.size(); i++ )
{
    cout << i << " = " << str[i] << endl;
}

Additionally, strings have a set of functions that we can use to manipulate, search, and otherwise work with them.

string name = "LUNA";
char letter;

size_t size() const;

The string's size() function will return the size of the string - how many characters are stored in the string. The size_t data type is just a type of integer - an unsigned integer, because sizes cannot be negative amounts.

Documentation: https://www.cplusplus.com/reference/string/string/size/

Example: Outputting a string's length

Let's write a little program that asks the user to enter some text, and then outputs the length of the string:

string text;
cout << "Enter some text: ";
getline( cin, text );
cout << "That string is " << text.size()
    << " characters long!" << endl;

When the user enters a line of text, it will count all characters (including spaces) in the string, so the text "cats dogs" would be 9 characters long.

Program output:

Enter some text: cats dogs
That string is 9 characters long!

Example: Counting z's

If we wanted to use a for loop to iterate over all the letters of an array, we could! Perhaps we want to count the amount of z's that show up:

string text;
int zCount = 0;

cout << "Enter some text: ";
getline( cin, text );

// Iterate from i=0 to the size of the string (not-inclusive)
for ( unsigned int i = 0; i < text.size(); i++ )
{
    // If this letter is a lower-case z or upper-case Z
    if ( text[i] == 'z' || text[i] == 'Z' )
    {
        // Add one to z count
        zCount++;
    }
}

// Display the result
cout << "There were " << zCount
    << " z(s) in the string!" << endl;

Program output:

Enter some text: The wizard fought a zombie lizard
There were 3 z(s) in the string!

string text = "a cat";

cout << text.size() << endl;

We can use the + operator to add strings together as well. This is called concatenation.

Let's say we have two strings we want to combine - favoriteColor and petName, we can use the concatenation operator + to build a new string, superSecurePassword.

string favoriteColor = "purple";
string petName = "Luna";
string superSecurePassword = favoriteColor + petName;
cout << superSecurePassword << endl; // = purpleLuna

We can also add onto strings by using the += operator. Let's say you're building a string over time in a program, and want to append parts separately.

string pizzaToppings = "";

// Later on...
pizzaToppings += "Buffalo sauce, ";

// Later on...
pizzaToppings += "Cheese, ";

// Later on...
pizzaToppings += "Pineapple";

// Later on...
cout << pizzaToppings << endl;

At the end of the program, the value of pizzaToppings would be:

"Buffalo sauce, Cheese, Pineapple"

string str1 = "t";
string str2 = "e";
string str3 = "a";

cout << str3 + str1 + str2 << endl;

size_t find (const string& str, size_t pos = 0 ) const;

The find function can be used to look for a substring in a bigger string. If the substring is found, its position is returned. Otherwise, the value of string::npos is found.

When a starting pos is included, it only begins the search at that position. If left off, it defaults to 0 (the start of the string).

Documentation: https://www.cplusplus.com/reference/string/string/find/

So when we want to search a string for some text, we can call it like bigString.find( findMeString ), and that function call will return an unsigned integer: the location of the findMeString within bigString, or the value of string::npos when it is not found.

string str = "this was written during the 2021 winter storm make it stop please.";

string findMe = "winter";

size_t position = str.find( findMe );

cout << "The text \"" << findMe
    << "\" was found at position " << position << endl;

Program output:

The text "winter" was found at position 33

string text = "The quick brown fox jumps over the lazy dog.";

0    1    2    3    4    5    6    7    8    9    10   11   12   13
-------------------------------------------------------------------
T    h    e         q    u    i    c    k         b    r    o    w

14   15   16   17   18   19   20   21   22   23   24   25   26   27   28
------------------------------------------------------------------------
n         f    o    x         j    u    m    p    s         o    v    e

29   30   31   32   33   34   35   36   37   38   39   40   41   42   43
------------------------------------------------------------------------
r         t    h    e         l    a    z    y         d    o    g    .

cout << text.find( "fox" ) << endl;

string substr (size_t pos = 0, size_t len = npos) const;

Returns a string within the string, starting at the position pos provided, and with a length of len.

Documentation: https://www.cplusplus.com/reference/string/string/substr/

With the substr() function, we can pull part of a string out, using a starting point and a length.

string text = "Name: Bob";

int start = 6;
int length = 3;

string name = text.substr( start, length );

cout << "Extracted \"" << name << "\"." << endl;

Program output:

Extracted "Bob".

string text = "Once upon a time...";

0    1    2    3    4    5    6    7    8    9    10   11   12   13   14   15   16   17   18
---------------------------------------------------------------------------------------------
O    n    c    e         u    p    o    n         a         t    i    m    e    .    .    .

cout << text.substr( 5, 4 ) << endl;

int compare (const string& str) const;

This compares the string with str and returns an integer:

• \(0\) is returned if both strings are the same.
• \(< 1\) (a negative number) is returned if the caller string is "less-than" the str string.
• \(> 1\) (a positive number) is returned if the caller string is "greater-than" the str string.

One character is "less than" another if it comes before, and it is "greater than" if it comes after, alphabetically.

(Remember that lower-case and upper-case letters are considered separate, so comparing 'a' to 'A' would actually return a positive number.)

Documentation: https://www.cplusplus.com/reference/string/string/compare/

string first;
string second;

cout << "Enter first string: ";
cin >> first;

cout << "Enter second string: ";
cin >> second;

int order = first.compare( second );

cout << endl << "Result: " << order << endl;

Program output:

Enter first string: apple
Enter second string: banana

Result: -1

string strAlchemy = "ALCHEMY";
string strMoose = "MOOSE";
string strXylophone = "XYLOPHONE";

string& insert (size_t pos, const string& str);

This function will take the calling string and modify it by inserting the string str at the position pos.

Documentation: https://www.cplusplus.com/reference/string/string/insert/

string text = "helloworld";

cout << "Original text: " << text << endl;

int start;
string insertText;

cout << "Enter text to insert: ";
getline( cin, insertText );

cout << "Enter position to insert: ";
cin >> start;

text = text.insert( start, insertText );

cout << endl << "String is now: " << text << endl;

Program output:

Original text: helloworld
Enter text to insert: -to the-
Enter position to insert: 5

String is now: hello-to the-world

string text = "crding";

cout << text.insert( 2, "ow" ) << endl;

string& erase (size_t pos = 0, size_t len = npos);

This function will return a string with a portion erased, starting at position pos and pulling out a length of len.

Documentation: https://www.cplusplus.com/reference/string/string/erase/

string text = "helloworld";

cout << "Original text: " << text << endl;

int start;
int length;

cout << "Enter position to begin erasing: ";
cin >> start;

cout << "Enter length of text to erase: ";
cin >> length;

text = text.erase( start, length );
cout << endl << "String is now: " << text << endl;

Program output:

Original text: helloworld
Enter position to begin erasing: 2
Enter length of text to erase: 5

String is now: herld

string text = "nowhere";

cout << text.erase( 0, 3 ) << endl;

string& replace (size_t pos, size_t len, const string& str);

This function is similar to erase, except it will insert the string str in place of the erased text.

Documentation: https://www.cplusplus.com/reference/string/string/replace/

string text = "helloworld";

cout << "Original text: " << text << endl;

int start;
int length;
string replaceWith;

cout << "Enter string to replace with: ";
getline( cin, replaceWith );

cout << "Enter position to begin replacing: ";
cin >> start;

cout << "Enter length of text to replacing: ";
cin >> length;

text = text.replace( start, length, replaceWith );
cout << endl << "String is now: " << text << endl;

Program output:

Original text: helloworld
Enter string to replace with: BYE
Enter position to begin replacing: 2
Enter length of text to replacing: 5

String is now: heBYErld

string text = "hopeless";

cout << text.replace( 4, 4, "ful" ) << endl;