C++ structure

structure (struct) are used to combine multiple data into single unit. That is reliable to create user defined data type. c++ are allowing to use data members and member function within the structures. there are declared using of this syntax.

struct tag_name{
  //data_members;
  //functions(){}
}variable_list;

for example

//structure of Book
struct Books{
  char  name[30],
  author[30],
  serial_number[20];
  int  pages;
  float weight,price;
}book;

//structure of Employee
struct Employee{
  char first_name[30],
      middle_name[30];
  int age;
  float salary;
}employee;

In above we are declare two structures Book and employee. struct is an keyword followed by its name. Curly braces are used to defined its body and this are terminated by semicolon. inside of structure declare variables and function those are used by structure variable and pointer. let view one example.

#include<iostream>
#include <string>
using namespace std;
//structure of Book
struct Book{
  string name,
  author,
  serial_number;
  int  pages;
  float weight,price;
}book;
int main(){
  //assign Book structure variable book values
  book.name="C++ Programming";
  book.author="Me and You";
  book.serial_number="oo7";
  book.pages=101;
  book.weight=250.59f;//gm
  book.price=1000.12f;

  //display values
  cout<<"Display Book information"<<endl;
  cout<<"name :"<<book.name<<endl;
  cout<<"author :"<<book.author<<endl;
  cout<<"pages :"<<book.pages<<endl;
  cout<<"serial_number :"<<book.serial_number<<endl;
  cout<<"weight :"<<book.weight<<endl;
  cout<<"price :"<<book.price<<endl;
  return 0;
}

Output

Display Book information
name :C++ Programming
author :Me and You
pages :101
serial_number :oo7
weight :250.59
price :1000.12

Note that help of struct variable and dot operator to access the data member value.

Why use structure

why use structure there question are arise in your mind. they are really useful to combine predefined and user defined data. for example array are used to store similar data. but array are not capable to store multiple different data. like student information (name,address,age,enrollment and so on). structures are suitable in this case.

Array of structure

When we declare an structure of our program then there are possible to create array of structure variables. for example suppose we are create an student structure then we can create array of structure in using of this syntax.

 struct_variable[size_of_array];

Let view an example.

//example of structure
#include<iostream>
#include <string>
using namespace std;
//structure of Book
struct Student{
  string name;
  int age;
};
int main(){
  //record is Array of 3 Students
  Student record[3];
  //you can use loop and insert values
  
  //array of record[0]
  record[0].name="foo";
  record[0].age=19;

  //array of record[1]
  record[1].name="bar";
  record[1].age=21;

  //array of record[2]
  record[2].name="woo";
  record[2].age=20;

  //display all record structure values
  for(int index=0;index<3;index++){
    cout<<"record["<<index<<"]"<<endl;
    cout<<"name: "<<record[index].name<<" age: "<<record[index].age<<endl;
  }
  
  return 0;
}

Output

record[0]
name: foo age: 19
record[1]
name: bar age: 21
record[2]
name: woo age: 20

structure of functions in c++

There are possible to defined function inside a structure in c++ programming. There is new features this are not possible in c programming.

//example of structure function
#include<iostream>
#include <string>
using namespace std;
//structure of Calculate
struct Calculate{
  int result;
   /*----
    sum is structure function
    accepts two integers value.
   */
   void sum(int num1,int num2){
    result=num1+num2;
    cout<<"Sum ("<<num1<<"+"<<num2<<") :"<<result<<endl;
   }
};
int main(){
  //Create structure variables
  Calculate operation;
  //access structure function
  operation.sum(12,32);
  operation.sum(10,20);
  return 0;
}

Output

Sum (12+32) :44
Sum (10+20) :30

Note that using dot(.) operator access the structure function.

structure Vs class

Nested structure

C++ are allowed to define one structure inside another structure. This process is called nested structure.help of nested structure we can solve complex task in very efficiently.

struct outer{
  //data member & functions
  struct inner{
     //data member & functions
  }inner_var;
}outer_var;

look at view example

//structure of Company
struct Company{
  //data member
  int company_code;
  /*company has department section*/
  struct departments
  { //data member
    int department_id;
    /*department has sale section*/
    struct sales
    {
      //logical code
    }sale;
    /*department has sale section*/
    struct accounts
    {
      //defined operation and logic 
    }account;//variable of structure
      
  }department;
  struct employees
  {   //function of employee structure
    void salary(int id){
      //logic code
    }
  }employee;
}my_company;

View a program to access struct data member and functions.

//example of nested structure in c++
#include<iostream>
using namespace std;
//structure of Company
struct Company{
  //data member
  int company_code;
  /*company has department section*/
  struct departments
  { //data member
    int department_id;
    /*department has sale section*/
    struct sales
    {
      void sales_list(){
        cout<<"This is sales_list function"<<endl;
      }
      //logical code
    }sale;
    /*department has sale section*/
    struct accounts
    {
      void get_amount(){
        cout<<"This is get_amount function"<<endl;
      }
      //defined operation and logic 
    }account;//variable of structure
      
  }department;
  struct employees
  {   //function of employee structure
    void salary(int id){
      cout<<"This is get_amount function"<<endl;
    }
  }employee;
}my_company;

int main(){
  /*
  access nested member function using of structure
  variables and dot operator. let example.
  */
  my_company.department.sale.sales_list();
  my_company.department.department_id=10;
  cout<<"department_id :"<<my_company.department.department_id<<endl;

  //try to access other function 
  return 0;
}

Output

This is sales_list function
department_id :10

There are most important to declare inner structure variable. because help of structure variable there are possible to access all data members and function.