Why Use Structures in C programming language

We have seen earlier how ordinary variables can hold one piece of information and how arrays can hold a number of pieces of information of the same data type. These two data types can handle a great variety of situations. But quite often we deal with entities that are collection of dissimilar data types.

For example, suppose you want to store data about a book. You might want to store its name (a string), its price (a float) and number of pages in it (an int). If data about say 3 such books is to be stored, then we can follow two approaches:

(a) Construct individual arrays, one for storing names, another for storing prices and still another for storing number of pages.

(b) Use a structure variable.

Let us examine these two approaches one by one. For the sake of programming convenience assume that the names of books wouldbe single character long. Let us begin with a program that uses arrays.

main( )

{

char name[3] ;

float price[3] ;

int pages[3], i ;

printf ( "\nEnter names, prices and no. of pages of 3 books\n" ) ;

for ( i = 0 ; i <= 2 ; i++ )

scanf ( "%c %f %d", &name[i], &price[i], &pages[i] );

printf ( "\nAnd this is what you entered\n" ) ;

for ( i = 0 ; i <= 2 ; i++ )

printf ( "%c %f %d\n", name[i], price[i], pages[i] );

}

And here is the sample run...

Enter names, prices and no. of pages of 3 books

A 100.00 354

C 256.50 682

F 233.70 512

And this is what you entered

A 100.000000 354

C 256.500000 682

F 233.700000 512

This approach no doubt allows you to store names, prices and number of pages. But as you must have realized, it is an unwieldy approach that obscures the fact that you are dealing with a group of characteristics related to a single entity—the book

The program becomes more difficult to handle as the number of items relating to the book go on increasing. For example, we would be required to use a number of arrays, if we also decide to store name of the publisher, date of purchase of book, etc. To solve this problem, C provides a special data type—the structure.

A structure contains a number of data types grouped together. These data types may or may not be of the same type. The following example illustrates the use of this data type.

main( )

{

struct book

{

char name ;

float price ;

int pages ;

} ;

struct book b1, b2, b3 ;

printf ( "\nEnter names, prices & no. of pages of 3 books\n" ) ;

scanf ( "%c %f %d", &b1.name, &b1.price, &b1.pages ) ;

scanf ( "%c %f %d", &b2.name, &b2.price, &b2.pages ) ;

scanf ( "%c %f %d", &b3.name, &b3.price, &b3.pages ) ;

printf ( "\nAnd this is what you entered" ) ;

printf ( "\n%c %f %d", b1.name, b1.price, b1.pages ) ;

printf ( "\n%c %f %d", b2.name, b2.price, b2.pages ) ;

printf ( "\n%c %f %d", b3.name, b3.price, b3.pages ) ;

}

And here is the output...

Enter names, prices and no. of pages of 3 books

A 100.00 354

C 256.50 682

F 233.70 512

And this is what you entered

A 100.000000 354

C 256.500000 682

F 233.700000 512

This program demonstrates two fundamental aspects of structures:

(a) declaration of a structure

(b) accessing of structure elements

Let us now look at these concepts one by one.