structures. parallel arrays inventory –one array keeps track of cost –one array keeps track of...
Post on 21-Dec-2015
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TRANSCRIPT
Structures
Parallel Arrays
• Inventory– One array keeps track of cost– One array keeps track of number in inventory
• What if there were many parallel items to keep track of?
• Would you want to keep track of 10, 20, 30 parallel arrays? Why not?
Structures
• Group many record items into one element
Inventory:
Item Name: Shirt
Item Number: 1232
Cost: $20.00
Num in Inventory: 10
Structures
typedef struct {char name[20];
int number;
double cost;
int num_in_inventory;
} inventory_item_t;
Structures
typedef struct {type name;…type name;
} struct_type;
• goes after #include and #define – not inside of main• type can be another structure data typetypedef struct {
char first[20];char last[20];
} name_t;typedef struct {
name_t name;int id;
} student_t;
Declaring and Initializing
• typedef does not allocate any memory
inventory_item_t shirts;
.name
.number
.cost
.num_in_inventory
…
Declaring and Initializing
shirts.number = 1232;
shirts.cost = 20.00;
shirts.num_in_inventory = 10;
//name???
.name
.number
.cost
.num_in_inventory
1232
20.00
10
…
Declaring and Initializing
shirts.number = 1232;
shirts.cost = 20.00;
shirts.num_in_inventory = 10;
strcpy(shirts.name, “Shirt”);
.name
.number
.cost
.num_in_inventory
1232
20.00
10
…
Accessing
• Print “There are 10 of item: shirt left in the inventory.”
Accessing
• Print “There are 10 of item: shirt left in the inventory.”
printf(“There are %d of item: %s left in the inventory”, shirts.num_in_inventory, shirts.name);
Structures and Functions
• Write a function to print all information about an inventory item
Structures and Functions
• Write a function to print all information about an inventory item
void print_item(inventory_item_t item) {
printf(“Item: %s\n”, item.name);
printf(“Item Number: %d\n”, item.number);
printf(“Cost: %lf\n”, item.cost);
printf(“Number Remaining: %d\n”, item.num_in_inventory);
}
Structures and Functions
• Call the function
inventory_item_t shirts;
…
print_item(shirts);
Structures as Output Parameters
• Write a function to “sell” an item by deducting 1 from the number of the item left in the inventory
• Return 1 if the sell was successful – 0 otherwise
• How would we call this function?
Structures as Output Parameters
• How would we call this function?
inventory_item_t shirts;
…
sell_item(shirts); //OK?
Structures as Output Parameters
• How would we call this function?
inventory_item_t shirts;int sell_ok;…sell_ok = sell_item(&shirts); if(sell_ok) {
printf(“Item sold\n”);} else {
printf(“Problem encountered! Item not sold.\n”);}
Structures as Output Parameters
int sell_item(inventory_item_t *to_sell) {int sell_ok;if((*to_sell).num_in_inventory > 0) {
//(*to_sell) is important!(*to_sell).num_in_inventory = (*to_sell).num_in_inventory –
1;sell_ok = 1;
} else {sell_ok = 0;
}return (sell_ok);
}
Component Selection Operator
• (*to_sell).num_in_inventory is the same as to_sell->num_in_inventory
int sell_item(inventory_item_t *to_sell) {int sell_ok;if(to_sell->num_in_inventory > 0) {
to_sell->num_in_inventory = to_sell->num_in_inventory – 1;sell_ok = 1;
} else {sell_ok = 0;
}return (sell_ok);
}
Returning a Structure
inventory_item_t getItem() {inventory_item_t new_item;printf(“Enter name:”);scanf(“%s”, new_item.name);printf(“Enter number:”);scanf(“%d”, &new_item.number);printf(“Enter cost:”);scanf(“%lf”, &new_item.cost):printf(“Enter number in inventory:”);scanf(“%d”, %new_item.num_in_inventory);return (new_item);
}
Arrays of Structures
inventory_item_t items[20];
• Access the name of item 5
Arrays of Structures
inventory_item_t items[20];
• Access the name of item 5items[4].name;
items[4].num_in_inventory = items[4].num_in_inventory – 1;
items[5].cost = 105.99;
scan_item(&items[10);