C Structures

Structs

When programming, it is often convenient to have a single name with which to refer to a group of a related values. Structures provide a way of storing many different values in variables of potentially different types under the same name.

Example 1

struct database 
{
  int id_number;
  int age;
  float salary;
};
 
int main()
{
  struct database employee;  /* There is now an employee variable that has
                              modifiable variables inside it.*/
  employee.age = 22;
  employee.id_number = 1;
  employee.salary = 12000.21;
}

Example 2

#include <stdio.h>
 
struct xampl {
  int x;
};
 
int main()
{  
    struct xampl structure;
    struct xampl *ptr;
 
    structure.x = 12;
    ptr = &structure; /* Yes, you need the & when dealing with 
                           structures and using pointers to them*/
    printf( "%d\n", ptr->x );  /* The -> acts somewhat like the * when 
                                   does when it is used with pointers
                                    It says, get whatever is at that memory
                                   address Not "get what that memory address
                                   is"*/
    getchar();
}

Unions

Unions are like structures except that all the variables share the same memory. When a union is declared the compiler allocates enough memory for the largest data-type in the union.