TYPEDEF - create variables by your name

Typedef:

          Typedef is a keyword used to assign new names to existing data types. This is same like defining alias for the commands.

typedef  existing_name alias_name;

After this statement, instead of existing_name we can use alias_name.

If we look at an example

          typedef int aj;

aj i , j;

The above statement define a term  aj  for an int type. Now this  aj  identifier can be used to define int type variables. This is also equal to int i , j;

          typedef unsigned long  int  ajj;

        ajj  i, j ;

After this type definition, the identifier ajj can be used as an abbreviation for the type unsigned long int.

Using typedef with structures :

You can use typedef to give a name to user defined data type as well. For example you can use typedef with structure to define a new data type and then use that data type to define structure variables directly as follows:

typedef struct book

{

           int x;

           float y;

           char c[10];

} Book;

         

         Here Book is the structure_variable name and book is tag_name. After this definition, we can create structure variables with Book word instead of struct book.

For example:

 #include <stdio.h>

 #include <string.h>

 typedef struct Books

 {

          char title[20];  

          int pages;

 } Book;

int main( )

           {

           Book  book;

           strcpy (book.title, "C Programme");

                     book.pages = 230;

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

           printf( "no of pages : %d\n", book.pages);

                     return 0;

           }

In the above program we have defined Book book instead of struct books book.

·       Typedef can be used for pointers also.

                    typedef int *x , y;

By this definition, we can use x for defining pointer variables and y can be used for integer variables.

#include <stdio.h>

 #include <string.h>

int main( )

     {

              typedef int  *x , y;

              y  a = 10;

              x  b;

              b = &a;

              printf("%d",a);              //output : 10 10

              printf("%d",*b);

               return 0;

     }