Structures and Unions

Structures and Unions

Introduction to Structure

A structure is a collection of one or more variables, possibly of different data types (e.g., int, float, char), grouped under a single name for convenient handling. Structures help to organize data, particularly in large programs, because they allow a group of related variables to be treated as a single unit.

The keyword struct introduces a structure declaration, which is a list of declarations enclosed in braces.

struct employee  
{  
char name[35];  
unsigned int age;  
char address[50];  
float salary;  
} emp1, emp2;

Initialization of Structure

Like other variables and arrays, structure variables can also be initialized where they are declared. To initialize structure variables, we list the values for the individual members separated by commas and enclosed in braces.

struct employee  
{  
char name[35];  
unsigned int age;  
char address[50];  
float salary;  
} emp1={"alpha",20,"Kathmandu",15000.00}, emp2={"beta", 25,"Bhaktapur", 20000.00};  
struct employee emp3={"gamma",25,"Lalitpur", 25000.00}

Size of Structure

A structure is a collection of multiple variables of different types. The compiler automatically does the structure padding to ensure all its members are byte-aligned, which means they are always stored in a continuous memory location.

struct employee  
{  
char name[35];  
unsigned int age;  
char address[50];  
float salary;  
}

In the above program, as we know char takes 1 byte and since it is a character array of size 35 so 1 character takes 1 byte, i.e, 35 bytes.

Accessing a member of a structure

Structure members are accessed using dot[.] operator which is also called “Structure member Operator”.
Suppose;

printf("The employee's name is %s",emp1.name);

Array of Structure

A collection of similar types of structures placed in a common variable name is called an array of structure.

C Program to store a record of 100 books.

#include<stdio.h>  
#include<conio.h>  
struct book  
{  
  char name[50];  
  float price;  
  int pages;  
};  
void main()  
{  
  struct book b[100];  
  float temp;  
  int i;  
  for(i=0;i<100;i++)  
  {  
  printf("\nEnter name:");  
  scanf("%s", b[i].name);  
  printf("\nEnter price:");  
  scanf("%f",&temp);  
  b\[i\].price=temp;  
  printf("\nEnter pages:");  
  scanf("%d", &b[i].pages);  
  }  
  for(i=0;i<100;i++)  
  {  
  printf("\nName:%s\tPrice:%f\tPages:%d",b[i].name,b[i].price,b[i].pages);  
  }  
getch();  
}  

Difference Between Array and Structure:

Union: Definition and Declaration

A union is a user-defined type similar to structure except for one key difference. A union is a special data type available in C that allows storing different data types in the same memory location.

The format of the union statement is as follows:

union union_name  
{  
member definition;  
member definition;  
...  
member defination;  
} union_variables;

Difference Between: