Structures

Structure is a user defined data type available in C that allows to combine data items of different kinds.

Difference b/w Array And Structure:

Array is a collection of several different item of same type but structure hold several different item of different type.

Structure Syntax:

struct [structure tag] {

   member definition;

   member definition;

   ...

   member definition;

} [one or more structure variables]; 

Note:To define a structure, you must use the struct statement.

 At the end of the structure's definition, before the final semicolon, you can specify one or more structure variables but it is optional

Example:

struct Books {

   char  title[50];

   char  author[50];

   char  subject[100];

   int   book_id;

} book; {book is a variable,it is optional to declare here}

How to declare a variable of a structure?

Syntax:

struct  struct_name  var_name;

or

struct struct_name {

   DataType member1_name;

   DataType member2_name;

   DataType member3_name;

   …

} var_name;

C Code to understand the concept  of Structure:

#include <stdio.h>

#include <string.h>

struct Books {

   char  title[50];

   char  author[50];

   char  subject[100];

   int   book_id;

};

int main( ) {

   struct Books Book1;        /* Declare Book1 of type Book */

   struct Books Book2;        /* Declare Book2 of type Book */

   /* book 1 specification */

   strcpy( Book1.title, "C Programming");

   strcpy( Book1.author, "Nuha Ali"); 

   strcpy( Book1.subject, "C Programming Tutorial");

   Book1.book_id = 6495407;

   /* book 2 specification */

   strcpy( Book2.title, "Telecom Billing");

   strcpy( Book2.author, "Zara Ali");

   strcpy( Book2.subject, "Telecom Billing Tutorial");

   Book2.book_id = 6495700;

   /* print Book1 info */

   printf( "Book 1 title : %s\n", Book1.title);

   printf( "Book 1 author : %s\n", Book1.author);

   printf( "Book 1 subject : %s\n", Book1.subject);

   printf( "Book 1 book_id : %d\n", Book1.book_id);

   /* print Book2 info */

   printf( "Book 2 title : %s\n", Book2.title);

   printf( "Book 2 author : %s\n", Book2.author);

   printf( "Book 2 subject : %s\n", Book2.subject);

   printf( "Book 2 book_id : %d\n", Book2.book_id);

   return 0;

}

⇒C Compiler to run:https://goo.gl/bzuHcQ

Structure in C  as a function:

#include <stdio.h>

#include <string.h>

struct Books {

   char  title[50];

   char  author[50];

   char  subject[100];

   int   book_id;

};

/* function declaration */

void printBook( struct Books book );

int main( ) {

   struct Books Book1;        /* Declare Book1 of type Book */

   struct Books Book2;        /* Declare Book2 of type Book */

   /* book 1 specification */

   strcpy( Book1.title, "C Programming");

   strcpy( Book1.author, "Nuha Ali"); 

   strcpy( Book1.subject, "C Programming Tutorial");

   Book1.book_id = 6495407;

   /* book 2 specification */

   strcpy( Book2.title, "Telecom Billing");

   strcpy( Book2.author, "Zara Ali");

   strcpy( Book2.subject, "Telecom Billing Tutorial");

   Book2.book_id = 6495700;

   /* print Book1 info */

   printBook( Book1 );

   /* Print Book2 info */

   printBook( Book2 );

   return 0;

}

void printBook( struct Books book ) {

   printf( "Book title : %s\n", book.title);

   printf( "Book author : %s\n", book.author);

   printf( "Book subject : %s\n", book.subject);

   printf( "Book book_id : %d\n", book.book_id);

}

⇒C Compiler:https://goo.gl/bzuHcQ

Pointers to Structures:

You can define pointers to structures in the same way as you define pointer to any other variable −

struct Books *struct_pointer;

Now, you can store the address of a structure variable in the above defined pointer variable. To find the address of a structure variable, place the '&'; operator before the structure's name as follows −

struct_pointer = &Book1;

To access the members of a structure using a pointer to that structure, you must use the → operator as follows −

struct_pointer->title;

Let us re-write the above example using structure pointer.


#include <stdio.h>
#include <string.h>

struct Books {
   char  title[50];
   char  author[50];
   char  subject[100];
   int   book_id;
};

/* function declaration */
void printBook( struct Books *book );
int main( ) {

   struct Books Book1;        /* Declare Book1 of type Book */
   struct Books Book2;        /* Declare Book2 of type Book */

   /* book 1 specification */
   strcpy( Book1.title, "C Programming");
   strcpy( Book1.author, "Nuha Ali"); 
   strcpy( Book1.subject, "C Programming Tutorial");
   Book1.book_id = 6495407;

   /* book 2 specification */
   strcpy( Book2.title, "Telecom Billing");
   strcpy( Book2.author, "Zara Ali");
   strcpy( Book2.subject, "Telecom Billing Tutorial");
   Book2.book_id = 6495700;

   /* print Book1 info by passing address of Book1 */
   printBook( &Book1 );

   /* print Book2 info by passing address of Book2 */
   printBook( &Book2 );

   return 0;
}

void printBook( struct Books *book ) {

   printf( "Book title : %s\n", book->title);
   printf( "Book author : %s\n", book->author);
   printf( "Book subject : %s\n", book->subject);
   printf( "Book book_id : %d\n", book->book_id);
}



When the above code is compiled and executed, it produces the following result −

Book title : C Programming
Book author : Nuha Ali
Book subject : C Programming Tutorial
Book book_id : 6495407
Book title : Telecom Billing
Book author : Zara Ali
Book subject : Telecom Billing Tutorial

Book book_id : 6495700