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Setting up and using structures on the heap
Structures and Unions example from a Well House Consultants training course
More on Structures and Unions [link] Source code: sixteen.c Module: C209
#include <stdio.h>
#include <stdlib.h> /* A C Structure is a collection of variables that are held together containing linked or related information about something. If this sounds very much like an object without the associated code (methods), you're right ;-) */ #define MAXROOMS 5 /* We'll set up a structure called an "R" ... a pointer to it is a "ROOM" */ typedef struct { int roomno; float d_price; float s_price; char faces; } R, *ROOM ; /* A function into which we pass a pointer to a structure ... we can then access members within the structure using the -> notation */ float doubleoffset(ROOM current) { return current->d_price - current->s_price; } main() { ROOM honeymoon; /* A couple of pointers */ ROOM garden; float extrabrekkie; int roomcount; int k; roomcount = MAXROOMS; /* Allocate memory for a structure for each initial room */ honeymoon = calloc(roomcount,sizeof(R)); for (k=0; k<roomcount; k++) { (honeymoon+k)->roomno = k+1; (honeymoon+k)->d_price = 95.00; (honeymoon+k)->s_price = 85.00; (honeymoon+k)->faces = 'E'; if (k==0) (honeymoon+k)->faces = 'S'; if (k==4) (honeymoon+k)->faces = 'N'; } /* And extend that memory to allow for three garden rooms too */ honeymoon = realloc(honeymoon,(roomcount+3) * sizeof(R)); garden = honeymoon + roomcount; for (k=0; k<3; k++) { (garden+k)->roomno = k+21; (garden+k)->d_price = 65.00; (garden+k)->s_price = 45.00; (garden+k)->faces = 'W'; } roomcount += 3; /* Loop through ALL the rooms, outputting data from each of them */ for (k=0; k<roomcount; k++) { extrabrekkie = doubleoffset(honeymoon+k); printf("\nRoom number %d\n",(honeymoon+k)->roomno); printf("The room costs up to %.2f per night\n", (honeymoon+k)->d_price); printf("Single offset for this room - %.2f\n",extrabrekkie); printf("Looks %c \n",(honeymoon+k)->faces); } } /* Sample compile and output munchkin:capr grahamellis$ gcc -o sixteen sixteen.c munchkin:capr grahamellis$ ./sixteen Room number 1 The room costs up to 95.00 per night Single offset for this room - 10.00 Looks S Room number 2 The room costs up to 95.00 per night Single offset for this room - 10.00 Looks E Room number 3 The room costs up to 95.00 per night Single offset for this room - 10.00 Looks E Room number 4 The room costs up to 95.00 per night Single offset for this room - 10.00 Looks E Room number 5 The room costs up to 95.00 per night Single offset for this room - 10.00 Looks N Room number 21 The room costs up to 65.00 per night Single offset for this room - 20.00 Looks W Room number 22 The room costs up to 65.00 per night Single offset for this room - 20.00 Looks W Room number 23 The room costs up to 65.00 per night Single offset for this room - 20.00 Looks W munchkin:capr grahamellis$ */ Learn about this subject
This module and example are covered on the following public courses:
* Learning to Program in C * Learning to program in C and C++ * Programming in C * C and C++ Programming * Learning to program in C and C++ * C and C++ Programming Also available on on site courses for larger groups Books covering this topic
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