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C++ Primer Plus

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cout << "bouquet: " << bouquet.name << " for $";

cout << bouquet.price << endl;

choice = bouquet; // assign one structure to another

cout << "choice: " << choice.name << " for $";

cout << choice.price << endl;

return 0;

}

Here’s the output from the program in Listing 4.12:

bouquet: sunflowers for $12.49

choice: sunflowers for $12.49

As you can see, memberwise assignment is at work, for the members of the choice structure are assigned the same values stored in the bouquet structure.

You can combine the definition of a structure form with the creation of structure variables. To do so, you follow the closing brace with the variable name or names:

struct perks

{

int key_number;

char car[12];

} mr_smith, ms_jones; // two perks variables

You even can initialize a variable you create in this fashion:

struct perks

{

int key_number;

char car[12];

} mr_glitz =

{

7, // value for mr_glitz.key_number member

"Packard" // value for mr_glitz.car member

};

However, keeping the structure definition separate from the variable declarations usually makes a program easier to read and follow.

Another thing you can do with structures is create a structure with no type name. You do this by omitting a tag name while simultaneously defining a structure form and a variable:

struct // no tag

{

int x; // 2 members

int y;

} position; // a structure variable

This creates one structure variable called position. You can access its members with the membership operator, as in position.x, but there is no general name for the type. You can’t subsequently create other variables of the same type. This book doesn’t use that limited form of structure.

Aside from the fact that a C++ program can use the structure tag as a type name, C structures have all the features discussed so far for C++ structures, apart from the C++11 changes. But C++ structures go further. Unlike C structures, for example, C++ structures can have member functions in addition to member variables. But these more advanced features most typically are used with classes rather than structures, so we’ll discuss them when we cover classes, beginning with Chapter 10, “Objects and Classes.”

Arrays of Structures

The inflatable structure contains an array (the name array). It’s also possible to create arrays whose elements are structures. The technique is exactly the same as for creating arrays of the fundamental types. For example, to create an array of 100 inflatable structures, you could do the following:

inflatable gifts[100]; // array of 100 inflatable structures

This makes gifts an array of inflatables. Hence each element of the array, such as gifts[0] or gifts[99], is an inflatable object and can be used with the membership operator:

cin >> gifts[0].volume; // use volume member of first struct

cout << gifts[99].price << endl; // display price member of last struct

Keep in mind that gifts itself is an array, not a structure, so constructions such as gifts.price are not valid.

To initialize an array of structures, you combine the rule for initializing arrays (a brace-enclosed, comma-separated list of values for each element) with the rule for structures (a brace-enclosed, comma-separated list of values for each member). Because each element of the array is a structure, its value is represented by a structure initialization. Thus, you wind up with a brace-enclosed, comma-separated list of values, each of which itself is a brace-enclosed, comma-separated list of values:

inflatable guests[2] = // initializing an array of structs

{

{"Bambi", 0.5, 21.99}, // first structure in array

{"Godzilla", 2000, 565.99} // next structure in array

};

As usual, you can format this the way you like. For example, both initializations can be on the same line, or each separate structure member initialization can get a line of its own.

Listing 4.13 shows a short example that uses an array of structures. Note that because guests is an array of inflatable, guest[0] is type inflatable, so you can use it with the dot operator to access a member of the inflatable structure.

Listing 4.13. arrstruc.cpp

// arrstruc.cpp -- an array of structures

#include

struct inflatable

{

char name[20];

float volume;

double price;

};

int main()

{

using namespace std;