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);