Data structure

By: Unknown on 02:34

information structure is a gathering of information components gathered together under one name. These information components, known as parts, can have distinctive sorts and diverse lengths. Information structures could be proclaimed in C++ utilizing the accompanying sentence structure:
struct type_name {
member_type1 member_name1;
member_type2 member_name2;
member_type3 member_name3;
.
.
} object_names;

Where type_name is a name for the structure type, object_name can be a set of valid identifiers for objects that have the type of this structure. Within braces {}, there is a list with the data members, each one is specified with a type and a valid identifier as its name.
For example:

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struct product { int weight; double price; } ; product apple; product banana, melon;

This declares a structure type, called product, and defines it having two members: weight and price, each of a different fundamental type. This declaration creates a new type (product), which is then used to declare three objects (variables) of this type: apple, banana, and melon. Note how once product is declared, it is used just like any other type.

Right at the end of the struct definition, and before the ending semicolon (;), the optional field object_names can be used to directly declare objects of the structure type. For example, the structure objects apple, banana, and melon can be declared at the moment the data structure type is defined:

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struct product { int weight; double price; } apple, banana, melon;

In this case, where object_names are specified, the type name (product) becomes optional: struct requires either a type_name or at least one name in object_names, but not necessarily both.

It is important to clearly differentiate between what is the structure type name (product), and what is an object of this type (apple, banana, and melon). Many objects (such as apple, banana, and melon) can be declared from a single structure type (product).

Once the three objects of a determined structure type are declared (apple, banana, and melon) its members can be accessed directly. The syntax for that is simply to insert a dot (.) between the object name and the member name. For example, we could operate with any of these elements as if they were standard variables of their respective types:

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apple.weight apple.price banana.weight banana.price melon.weight melon.price

Each one of these has the data type corresponding to the member they refer to: apple.weight, banana.weight, and melon.weight are of type int, while apple.price, banana.price, and melon.price are of type double.

Here is a real example with structure types in action:

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// example about structures #include <iostream> #include <string> #include <sstream> using namespace std; struct movies_t { string title; int year; } mine, yours; void printmovie (movies_t movie); int main () { string mystr; mine.title = "2001 A Space Odyssey"; mine.year = 1968; cout << "Enter title: "; getline (cin,yours.title); cout << "Enter year: "; getline (cin,mystr); stringstream(mystr) >> yours.year; cout << "My favorite movie is:\n "; printmovie (mine); cout << "And yours is:\n "; printmovie (yours); return 0; } void printmovie (movies_t movie) { cout << movie.title; cout << " (" << movie.year << ")\n"; }

Enter title: Alien Enter year: 1979 My favorite movie is: 2001 A Space Odyssey (1968) And yours is: Alien (1979)

The example shows how the members of an object act just as regular variables. For example, the member yours.year is a valid variable of type int, and mine.title is a valid variable of type string.

But the objects mine and yours are also variables with a type (of type movies_t). For example, both have been passed to function printmovie just as if they were simple variables. Therefore, one of the features of data structures is the ability to refer to both their members individually or to the entire structure as a whole. In both cases using the same identifier: the name of the structure.

Because structures are types, they can also be used as the type of arrays to construct tables or databases of them:

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// array of structures #include <iostream> #include <string> #include <sstream> using namespace std; struct movies_t { string title; int year; } films [3]; void printmovie (movies_t movie); int main () { string mystr; int n; for (n=0; n<3; n++) { cout << "Enter title: "; getline (cin,films[n].title); cout << "Enter year: "; getline (cin,mystr); stringstream(mystr) >> films[n].year; } cout << "\nYou have entered these movies:\n"; for (n=0; n<3; n++) printmovie (films[n]); return 0; } void printmovie (movies_t movie) { cout << movie.title; cout << " (" << movie.year << ")\n"; }

Enter title: Blade Runner Enter year: 1982 Enter title: The Matrix Enter year: 1999 Enter title: Taxi Driver Enter year: 1976 You have entered these movies: Blade Runner (1982) The Matrix (1999) Taxi Driver (1976)

                                             
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