Jack has been asked to write a program to calculate the potential profit in a soft drinks business. The program will store the costs involved in producing and selling one litre of each drink.

Jack adapts the program to ensure that water cost can only be entered as always greater than or equal to £0.10 and less than or equal to £0.50 per litre.

State the standard algorithm that is used to ensure that data entered is acceptable. (1)

(Input) Validation (1 mark)