typdefs for pointer and function pointer and enum and struct

typedef in function pointer:

int add(int a, int b)
{
    return (a+b);
}

typedef int (*add_integer)(int, int); //declaration of function pointer

int main()
{
    add_integer addition = add; //typedef assigns a new variable i.e. 

                                //"addition" to original function "add"
    int c = addition(11, 11);   //calling function via new variable
    printf("%d",c);
    return 0;
}

Ref: https://stackoverflow.com/questions/1591361/understanding-typedefs-for-function-pointers-in-c

typedef in pointer:

The typedef may be used in declaration of a number of pointers of the same type. It does not change the type, it only creates a synonym, i.e., another name for the same type as illustrated below.

typedef float* FP; // Now FP represents float*

float x,y,z;

FP px =&x, py = &y, pz = &z ; // Use of FP

In the above code px, py, and pz are pointers initialized with addresses of x, y, and z respectively.

Illustrates use of typedef in pointer declaration.

#include <stdio.h>
void main()
{
   typedef double* Dp;
   double x = 10.5,y = 8.6, z = 12.5;
   Dp px = &x , py = &y, pz = &z;
   clrscr();
   printf("x = %.3lf,\t *px =  %.3lf\t px = %p \n", x, *px, px);
   printf("y = %.3lf,\t *py =  %.3lf\t py = %p \n", y, *py, py);
   printf("z = %.3lf,\t *pz =  %.3lf\t pz = %p \n", z, *pz, pz);
} 

Reference from:
http://ecomputernotes.com/what-is-c/function-a-pointer/typedef-in-pointer

typedef in enum:

way 1: 

enum State {Working = 1, Failed = 0}; 

way 2: 

typedef enum {false, true} boolean;

boolean error = false;
         

Reference from:
http://ecomputernotes.com/what-is-c/function-a-pointer/typedef-in-pointer

typedef in struct:

#include <stdio.h>
#include <string.h>
 
typedef struct Books {
   char title[50];
   char author[50];
   char subject[100];
   int book_id;
} Book;
 
int main( ) {

   Book book;
 
   strcpy( book.title, "C Programming");
   strcpy( book.author, "Nuha Ali"); 
   strcpy( book.subject, "C Programming Tutorial");
   book.book_id = 6495407;
 
   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);

   return 0;
}

Ref: https://www.tutorialspoint.com/cprogramming/c_typedef.htm