Structure in C++.

byComputer Programming and Technology. •
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Structure

  • A structure is a set of variable that can be the same, or different styles. 
  • You may use the dot (.) operator to refer to a structure as a single variable, and to its parts as members of that variable.  
  • The power of structures lies in the fact that once defined, the name of the structure becomes a user-defined type of data and may be used in the same way as other types of built-in data, such as int, double, char.
struct STUDENT
{
        int rollno, age;
        char name[80];
        float marks;
} ; 

#include<iostream.h>
#include<conio.h>
int main()
{
       // declare two variables of the new type
       STUDENT s1, s3;
       //accessing of data members
       cin>>s1.rollno>>s1.age>>s1.name>>s1.marks;
       cout<<s1.rollno<<s1.age<<s1.name<<s1.marks;
       //initialization of structure variable
       STUDENT s2 = {100,17,”Aniket”,92};
       cout<<s2.rollno<<s2.age<<s2.name<<s2.marks;
       //structure variable in assignment statement
       s3=s2;
       cout<<s3.rollno<<s3.age<<s3.name<<s3.marks;
       return 0; 
}

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Defining a structure

  • When dealing with the students in a school, many variables of different types are needed.  It may be necessary to keep track of name,  age, Rollno, and marks point for example.


struct STUDENT

{
        int rollno, age;
        char name[80];
        float marks;
}; 

  • STUDENT  is called the structure tag, and is your brand new data type, like int, double or char.
  • rollno, name, age, and marks are structure members.

Declaring Variables of Type struct

  • The most effective method to tackle structure variables is to describe the structure globally.  
  • It tells "the whole world" that a new type of data exists, namely, the key and any functions in the system.  
  • Place it BEFORE void main) (to declare a structure global.  
  • Then, for example, the structure variables can be described locally for example...

struct STUDENT
{

        int rollno, age;
        char name[80];
        float marks;
}; 

int main()
{
       // declare two variables of the new type
       STUDENT s1, s3;
       ………
       ………
       return 0; 
}

Alternate method of declaring variables of type struct:


struct STUDENT

{
        int rollno, age;
        char name[80];
        float marks;
} s1, s3;


Accessing of data members

  • The accessing of data members is done by using the following format:
  • structure variable.member name

for example
cin>>s1.rollno>>s1.age>>s1.name>>s1.marks;

Initialization of structure variable

Initialization is done at the time of declaration of a variable. For example
STUDENT s2 = {100,17,”Aniket”,92};
Structure variable in assignment statement
s3=s2; 
  • The statement assigns the value of each member of s2 to the corresponding member of s3. 
  • Note that one structure variable can be assigned to another only when they are of the same structure type, otherwise compiler will give an error.

Nested structure (Structure within structure)

  • It is possible to use a structure to define another structure. This is called nesting of structure. Consider the following program


struct DAY

{
     int month, date, year;
};

struct STUDENT
{
        int rollno, age;
        char name[80];
        day date_of_birth;
        float marks;
};

typedef

  • It is used to define new data type for an existing data type. 
  • It provides and alternative name for standard data type. 
  • It is used for self documenting the code by allowing descriptive name for the standard data type.

The general format is:
typedef existing datatype new datatype

for example:
typedef float real;Now, in a program one can use datatype real instead of float.
Therefore, the following statement is valid:
real amount;

Enumerated data type

  • The enum specifier defines the set of names which are stored internally as integer constant. The first name was given the integer value 0, the second value 1 and so on.
for example: 
enum months{jan, feb, mar, apr, may} ;
It has the following features:
  • It is user defined.
  • It works if you know in advance a finite list of values that a data type can take.
  • The list cannot be input by the user or output on the screen.

#define preprocessor directive


  • The #define preprocessor allows to define symbolic names and constants e.g.#define pi 3.14159 
  • This statement will translate every occurrence of PI in the program to 3.14159

Macros


  • Macros are built on the #define preprocessor. Normally a macro would look like:#define square(x) x*x 
  • Its arguments substituted for replacement text, when the macro is expanded.

C++ Program to assign data to members of a structure variable and display it.

#include <iostream.h>
#include <conio.h>
struct Person
{
    char name[50];
    int age;
    float salary;
};

int main()
{
    Person p1;
    
    cout << "Enter Full name: ";
    cin.get(p1.name, 50);
    cout << "Enter age: ";
    cin >> p1.age;
    cout << "Enter salary: ";
    cin >> p1.salary;

    cout << "\nDisplaying Information." << endl;
    cout << "Name: " << p1.name << endl;
    cout <<"Age: " << p1.age << endl;
    cout << "Salary: " << p1.salary;

    return 0;
}
Output

Enter Full name: mskuthar
Enter age: 27
Enter salary: 30240.4

Displaying Information.
Name: mskuthar
Age: 27
Salary: 30240.4
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