Structs and Array, Together

Chapter 9

Arrays in structs

Suppose we want to store a list of numbers in an array. However, the list may or may not fill up the entire array. We can create a struct for our list where we store the current length (or size) of the list.

• Two items are associated with a list:

  • Values (elements)
  • Length of the list

• Define a struct containing both items:

  // Max size of a list
  const int LIST_SIZE = 1000;
  
  /**
   * A data type that holds an array and its length
   */
  struct List
  {
      int values[LIST_SIZE]; // array containing list elements
      int length; // the number of values used in this list
  };

The members of intList after begin declared as a List.

Assignment

// variable declaration and initialization.
List intList {{}, 0}; // Set values all to 0 and length to 0.

// Set first value to 21.
intList.values[intList.length] = 21;
intList.length++; // update the length to 1

// Set second value to 117.
intList.values[intList.length] = 117;
intList.length++; // update the length to 2

The members of intList after initialization and assigning the first two values.

structs in Arrays

A common practice is to have arrays of structs. For example,

/**
 * Info about an employee of this company.
 */
struct Employee
{
    string firstName;
    string lastName;
    int    personID;
    string deptID;
    double yearlySalary;
    double yearToDatePaid;
};

Employee employees[50]; // variable declaration

// output first names
for (int index = 0; index < 50; ++index)
    cout << employees[index].firstName << endl;

Notice the order of the operations to access a name. Because employees is an array, first the array subscript operator employees[index] accesses one employee. Then, the member access operator .firstName is used to access that employee's first name.

structs within structs

structs may also be members of other structs. For example,

/**
 * A person's name.
 */
struct Name
{
    string first; 
    string middle;
    string last;
};

/**
 * A US address.
 */
struct Address
{
    string streetAddress;
    string city;
    string state;
    int zip;
};

/**
 * Info record of a customer.
 */
struct Customer
{
    int id;
    Name name;
    Address shippingAddress;
    Address billingAddress;
};

Customer newCustomer;
newCustomer.id = 2000;
newCustomer.name.first = "James";
newCustomer.name.last = "Kirk";
newCustomer.shippingAddress.city = "South Carolina";
//...

Again, notice the order in which the members are accessed from left to right. For example, to get a first name from newCustomer, we first access a name record and then the name's first member.

Summary

• structs can be members of other structs
• structs can have array members.
• Arrays can be of a struct type.