Inputs:

• UPC - from user
• Quantity - from user
• Cash Given - from user
• Store ID - from system (user's record)

Outputs:

• Instance of "inventory" to be decremented from Inventories
• Message to screen

Error conditions:

• Syntactically incorrect input(s)
• UPC does not exist
• Cash Given is negative

Algorithm:

display cashier interface

if inputs from user are syntactically correct then {
  if UPC does not exist then
    print_to_user `UPC does not exist'
    refresh form, break
  else
    while (Cash_Given < 0)
      print_to_user `Negative Cash Given!'
    refresh field
  endif
  Send new Quantity to be decremented to the data store
  (Inventories) to be updated

  update receipt (UPC, item, quantity)
  Total = Total + Inventory[Sales_Price]*entered_quantity
  Amount_Owing = Total - Cash_Given
  Change = Cash_Given - Total
else
  print_to_user `Syntax error in input(s)'
endif

return to the interface to allow user to choose other
options or go back to the main menu

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