5.1.2 Pairs

A pair is exactly how it sounds, it is a pair of values. Pairs can be two values of the same type, but they can also contain values of a different type. Pairs are often used to hold two pieces of related data. You will see pairs used later as you explore key/value pairs with maps.

Creating Pairs

Pairs are part of the C++ standard library and do not need a special import statement.

To declare a pair, you use the keyword pair and specify the two types of variables inside angled brackets and then the variable name.

Basic Form:

pair<type1, type2> variableName;

Examples:

pair<string, string> address;
pair<string, int> nameAge;
pair<double, double> math;

When creating the pair, you can assign initial values by placing them inside curly brackets.

Examples:

pair<string, int> nameAge {"Betsy", 9};
pair<double, double> math {5.3, 8.7};

Accessing and Updating Values

Accessing and updating values is similar to how values are accessed and updated with a struct. With structs, you access the value with a dot and the member name. Since a pair doesn’t have member variables, you simply access using the keywords first and second.

Example:

pair<string, string> address {"Richardson", "TX"};

cout << address.first << endl;
cout << address.second << endl;

Output:

Richardson
TX

Updates are done using the same access.

pair<string, int> nameAge {"Betsy", 9};
nameAge.second = 10;

Using Pairs

Just like any other data structure, pairs can be used as a separate data structure or as part of another data structure. In this example, you can see how pairs can be used with a vector or a queue.

Examples:

vector<pair<string, int> > classRoster;
queue<pair<string, string> > names;

As mentioned above, pairs will be used for specific purposes in C++, like maps. Beyond that, pairs do have limited use since it can often be just as easy and more descriptive to create a struct. For example, if you wanted to store the first and last name, you can do this with a pair and then represent the first name in the first position and the last name in the second position.

Alternatively, you can create a name struct and give the member names more descriptive values such as firstName and lastName.

Try This Example