C programming/Structures

Basic structrues

Example 1

Create and instantiate a structure

#include <stdio.h>
#include <stdlib.h>

struct coor {
  int x;
  int y;
};

int main( void ) {
  struct coor place;
  
  place.x = 17;
  place.y = 19;
  
  printf("Tallet er %i\n",place.x+place.y);
  return(0);
}

Example 2

Same as example 1, but using as typedef

#include <stdio.h>
#include <stdlib.h>

struct coor {
  int x;
  int y;
};

typedef struct coor coordinate;
int main( void ) {
  coordinate place;
  
  place.x = 17;
  place.y = 19;
  
  printf("Tallet er %i\n",place.x+place.y);
  return(0);
}

Example 3

In example 3 the memory is reserver with malloc and indirect addressing is used to access the structure.

#include <stdio.h>
#include <stdlib.h>

struct coor {
  int x;
  int y;
};

typedef struct coor coordinate;
int main( void ) {
  coordinate *place = malloc( sizeof( coordinate ) );

  (*place).x = 17;  /* One form of indirect addressing shown */
  place->y = 19;     /* Another form of indirect addressing shown */

  printf("Tallet er %i\n",place->x + place->y);
  free( place ); /* Always remember to free allocated memory (Good habbit)*/
  return( 0 );
}

Arrays of structures example

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define STUDENTS 16
#define FREE 0
#define POPULATE(FIELD, ID, NAME, SURNAME) class[FIELD].id = ID, \
                                          strcpy(class[FIELD].name,NAME), \
                                          strcpy(class[FIELD].surname,SURNAME)


struct person {
    int id;
    char name[25];
    char surname[25];
};

typedef struct person p;

int main( void ) {
    p class[ STUDENTS ];
        /* Initialize p*/
    int i;
    for ( i = 0; i < STUDENTS ; i++ ) {
        class[i].id = FREE;  /* 0 = No student allocated */
    }

    /* Populate class */
    class[0].id = 101; strcpy(class[0].name,"Henrik"); strcpy(class[0].surname,"Thomsen");
    class[7].id = 145; strcpy(class[7].name,"Anders"); strcpy(class[7].surname,"And");
    POPULATE(3,78,"Kaptajn","Haddock"); /* using macro POPULATE (Just for fun)*/


        /* Parse structure and print populated students */
    for ( i = 0; i < STUDENTS ; i++ ) {
        if ( class[i].id != FREE ) {
                printf("Student: ID: %i name: %s %s\n",class[i].id, class[i].name, class[i].surname);
                fflush(stdout); /* Empty buffer to stdout (Just for fun) */
        }
    }
}