/*example on structures  */
#include <stdio.h>
#include <string.h>


int main (void)
{
  /* define a structure template called mydetails */
  /* mydetails is the tagname */
  /* alternative methods are described at the bottom of this file */
  struct mydetails
  {
      char my_name[30], address1[30], address2[30], address3[30];
      int my_age;
  };
  
  /* the variable MD is of the form defined by mydetails */
  struct mydetails MD;
  
  /* now assign some values to the fields */
  strcpy(MD.my_name,"Christian Hicks");
  strcpy(MD.address1,"Stephenson Building");
  strcpy(MD.address2,"Claremont Road");
  strcpy(MD.address3,"Newcastle upon Tyne");
  MD.my_age = 42;
  
  /*next look at how to pass structures to functions by
  value or by reference */
  
  /*this procedure passes the structure by value */
  void printname(struct mydetails M)
  {
      printf("My name is = %s\n",M.my_name);
      printf("M.my_age = %i\n",M.my_age);
      printf("Address line 1 = %s\n",M.address1);
      printf("Address line 2 = %s\n",M.address2);
      printf("Address line 3 = %s\n",M.address3);
  }
  
  /*this procedure passes the structure by reference i.e. just
  the pointer. this is faster because only the pointer is copied */
  void printptrname(struct mydetails *p)
  {
      printf("pointer address is %p\n",p);
      printf("Address line 1 = %s\n",p->address1);
      printf("Address line 2 = %s\n",p->address2);
      printf("Address line 3 = %s\n",(*p).address3);
      printf("my age is %i\n",p->my_age);
     /*note the way that the field within the pointer is dereferenced */
     /* it can be done either by (*p). or p-> */
  }
  
  printname(MD);
  printptrname(&MD);
 
  printf("MD.my_age = %i\n",MD.my_age);
  /* the variable names is an array of mydetails */
  struct mydetails names[1000]; 
  /* the variable ptr is a pointer to a variable of type mydetails */
  struct mydetails *ptr;
}

/* there are some alternative ways of defining structures
  the first does not use a tag name:
  struct
  {
     char my_name[30], address1[30], address2[30], address3[30];
     int my_age;
  } variablename;
  
  The second uses a tag name and declares the variables:
  struct myname
  {
     char my_name[30], address1[30], address2[30], address3[30];
     int my_age;
  } variablename, vn2;
  
  The third method is to define the type using typedef:
  
  typedef struct
  {
     char my_name[30], address1[30], address2[30], address3[30];
     int my_age;
  } myname;
  
  we could then declare variables to be of the user defined type
  myname:
  
  myname v1,v2,v3;
  */