COMP1721 - Higher Computing 1B

1. #include <stdio.h>
   #include <stdlib.h>
   
   typedef struct purchase purchase;
   typedef struct item     item;
   typedef double          price;
   typedef long            barcode;
   
   struct purchase {
       item        *what;
       int         how_many;
       purchase    *next;
   };
   
   struct item {
       char    *item_name;
       price   item_price;
       barcode item_barcode;
       item    *next;
   };
   
   enum {
       MAX_INPUT_LINE_LENGTH = 1024
   };
   
   void print_bill(purchase *purchase_list);
   purchase *add_purchase(barcode code, purchase *purchase_list, item *item_list);
   purchase *find_purchase(item *i, purchase *purchase_list);
   item *add_item(item *item_list);
   item *find_item(barcode code, item *item_list);
   void *salloc(size_t size);
   void read_to_newline(void);
   
   int
   main(void) {
       char command[MAX_INPUT_LINE_LENGTH];
       purchase *purchase_list = NULL;
       item *item_list = NULL;
       
       printf("Kensington Kwiki-Mart Billing System\n");
       while (1) {
           printf("Enter Command: ");
           if (fgets(command, MAX_INPUT_LINE_LENGTH, stdin) == NULL)
               return 0;
           
           if (strcmp(command,"bill\n") == 0) {
               while (1) {
                   barcode code;
                   printf("Enter barcode: ");
                   scanf("%ld", &code);
                   read_to_newline();
                   if (code == 0)
                       break;
                   purchase_list = add_purchase(code, purchase_list, item_list);
               }
             print_bill(purchase_list);
           } else if (strcmp(command, "price\n") == 0) {
               item_list = add_item(item_list);
           } else {
               printf("Unknown command - legal commands are bill and price\n");
           }
       }
       return 0;
   }
   
   void
   print_bill(purchase *purchase_list) {
       price total = 0;
       purchase *p;
       
       for (p = purchase_list; p != NULL; p = p->next) {
           price x = p->how_many * p->what->item_price;
           total += x;
           printf("%dx %s @$%.2f = $%.2f\n", p->how_many, p->what->item_name, p->what->item_price, x);
       }
   
       printf("Total: $%.2f\n", total);
       printf("Thank for Shopping at Kensington Kwiki-Mart\n");
   }
   
   
   purchase *
   add_purchase(barcode  code, purchase *purchase_list, item *item_list) {
       purchase *p;
       item     *i;
       
       i = find_item(code, item_list);
       if (i == NULL) {
           fprintf(stderr, "Unknown barcode\n");
           return purchase_list;
       }
       
       p = find_purchase(i, purchase_list);
       
       if (p != NULL) {
           p->how_many++;
           return purchase_list;
       }
       
       p = salloc(sizeof (purchase));
       p->what = i;
       p->how_many = 1;
       p->next = purchase_list;
       return p;
   }
   
   purchase *
   find_purchase(item *i, purchase *purchase_list) {
       purchase *p;
       
       for (p = purchase_list; p != NULL; p = p->next)
           if (p->what == i)
               return p;
       
       return NULL;
   }
   
   item *
   add_item(item *item_list) {
       barcode code;
       char    buffer[MAX_INPUT_LINE_LENGTH];
       item    *i;
       
       printf("Enter barcode: ");
       scanf("%ld", &code);
       read_to_newline();
       i = find_item(code, item_list);
   
       if (i != NULL) {
           printf("Enter new price for %s: ", i->item_name);
           scanf("%lf", &(i->item_price));
           read_to_newline();
           return item_list;
       }
       
       i = salloc(sizeof (item));
       i->item_barcode = code;
       printf("Enter name of the item: ");
       if (fgets(buffer, MAX_INPUT_LINE_LENGTH, stdin) == NULL || strlen(buffer) == 0) {
           fprintf(stderr, "Can not read name\n");
           exit(1);
       }
       buffer[strlen(buffer) - 1] = '\0'; /* remove '\n' */
       i->item_name = salloc(strlen(buffer) + 1);
       strcpy(i->item_name, buffer);
       printf("Enter price: ");
       scanf("%lf", &(i->item_price));
       read_to_newline();
       i->next = item_list;
       return i;
   }
       
   item *
   find_item(barcode code, item *item_list) {
       item *i;
       for (i = item_list; i != NULL; i = i->next) {
           if (i->item_barcode == code)
               return i;
       }
       return NULL;
   }
   
   void *
   salloc(size_t size) {
       void *m = malloc(size);
       if (m == NULL) {
           fprintf(stderr, "postcode_server: out of memory - attempting to malloc %d bytes\n", (int)size);
           exit(1);
       }
       return m;
   }
   
   void
   read_to_newline(void) {
       int c;
       while (1) {
           c = getchar();
           if (c == '\n' || c == EOF)
               return;
       }
   }