C Structures

C Structures

In programming, we usally deal with collection of ints, chars and floats rather than isolated entities.

Example an entity book is a collection of things like a title, an author, total pages, date of publication and price etc..

Structure is user defined data type which combines dissimilar data types into an entity.

Strucure syntax,

struct <name>
{
  //data-type member1;
  //data-type member2;
  ...
  //data-type membern;
};

Sample c program which defines the structure for book entity, reads the mutiple structure variables and prints the each structure variable of the book entity.

#include<stdio.h>                                                               
                                                                                
void main()                                                                     
{                                                                               
  struct book                                                                   
  {                                                                             
    int id;                                                                     
    char title[30], author[40];                                                 
    float price;                                                                
  };                                                                            
  struct book b1, b2, b3;                                                       
                                                                                
  printf("Enter book id, title, auther and price \n");                          
  scanf("%d %s %s %f", &b1.id, b1.title, b1.author, &b1.price);                 
  scanf("%d %s %s %f", &b2.id, b2.title, b2.author, &b2.price);                 
  scanf("%d %s %s %f", &b3.id, b3.title, b3.author, &b3.price);                 
                                                                                
  printf("\nbook id\ttitle \t auther \t price \n");                             
  printf("%d\t%s\t%s\t%f\n", b1.id, b1.title, b1.author, b1.price);             
  printf("%d\t%s\t%s\t%f\n", b2.id, b2.title, b2.author, b2.price);             
  printf("%d\t%s\t%s\t%f\n", b3.id, b3.title, b3.author, b3.price);             
} 

Output:

$ cc structure.c
$ ./a.out 
Enter book id, title, auther and price 
1
book1
author1
30
2
book2
author2
40
3
book3
author3
55

book id	title 	 auther 	 price 
1	book1	author1	30.000000
2	book2	author2	40.000000
3	book3	author3	55.000000

book structure has different data type members like int, string and float.

Creates the multiple structure variable b1, b2 and b3.

Reads the input for each structure variables and prints the each structure variable as row.

Structure declaration and variable initialization.

this c program explains how to declare the structure and create structure variable definition.

#include<stdio.h>                                                            
                                                                                
void main()                                                                     
{                                                                               
  struct book                                                                   
  {                                                                             
    int id;                                                                     
    char title[30], author[40];                                                 
    float price;                                                                
  };                                                                            
  struct book b1 = {1, "book1", "author1", 20.5};                               
                                                                                
  printf("\nbook id\ttitle \t auther \t price \n");                             
  printf("%d\t%s\t%s\t%f\n", b1.id, b1.title, b1.author, b1.price);             
} 

Output:

$ cc structure.c
$ ./a.out 
$ cc structure.c
$ ./a.out 

book id	title 	 auther 	 price 
1	book1	author1	20.500000

Structure declaration and structure variable as one statment

In C programming, we can also combine structure declaration and structure variable definition in one statement instead of doing as above.

#include<stdio.h>                                                              
                                                                                
void main()                                                                     
{                                                                               
  struct book                                                                   
  {                                                                             
    int id;                                                                     
    char title[30], author[40];                                                 
    float price;                                                                
  }b1 = {1, "book1", "author1", 20.5};                                          
                                                                                
  printf("\nbook id\ttitle \t auther \t price \n");                             
  printf("%d\t%s\t%s\t%f\n", b1.id, b1.title, b1.author, b1.price);             
}  

Output:

$ cc structure.c
$ ./a.out 
$ cc structure.c
$ ./a.out 

book id	title 	 auther 	 price 
1	book1	author1	20.500000

Structure variable copy

In c programming, the value of one structure variable can be copied to another same structure variable using assignment operator.

#include<stdio.h>                                                             
                                                                                
void main()                                                                     
{                                                                               
  struct book                                                                   
  {                                                                             
    int id;                                                                     
    char title[30], author[40];                                                 
    float price;                                                                
  }b2, b1 = {1, "book1", "author1", 20.5};  
  
  // structure variable copy
  b2 = b1;                                                                      
                                                                                
  printf("\nbook id\ttitle \t auther \t price \n");                             
  printf("%d\t%s\t%s\t%f\n", b1.id, b1.title, b1.author, b1.price);             
  printf("%d\t%s\t%s\t%f\n", b2.id, b2.title, b2.author, b2.price);             
}   

Output:

$ cc structure.c
$ ./a.out 

book id	title 	 auther 	 price 
1	book1	author1	20.500000
1	book1	author1	20.500000

Both structure variable will be impacted when updating after copy

If we update one of the structure variable after copy statement, both structure variable will not be impacted.

#include<stdio.h>                                                             
                                                                                
void main()                                                                     
{                                                                               
  struct book                                                                   
  {                                                                             
    int id;                                                                     
    char title[30], author[40];                                                 
    float price;                                                                
  }b2, b1 = {1, "book1", "author1", 20.5};                                      
  b2 = b1;                                                                      
  b2.price = 35.0;                                                              
  printf("\nbook id\ttitle \t auther \t price \n");                             
  printf("%d\t%s\t%s\t%f\n", b1.id, b1.title, b1.author, b1.price);             
  printf("%d\t%s\t%s\t%f\n", b2.id, b2.title, b2.author, b2.price);             
}  

Output:

$ cc structure.c
$ ./a.out 

book id	title 	 auther 	 price 
1	book1	author1	20.500000
1	book1	author1	35.000000