The calculator has a stack that can contain real numbers. • The calculator waits for user input and expects to receive strings containing whitespace separated lists of numbers and operators. • Numbers are pushed on to the stack. Operators operate on numbers that are on the stack. • Available operators are +, -, , /, sqrt, undo, clear. • Operators pop their parameters off the stack, and push their results back onto the stack. • The ‘clear’ operator removes all items from the stack. • The ‘undo’ operator undoes the previous operation. “undo undo” will undo the previo us two operations. • sqrt performs a square root on the top item from the stack. • The ‘+’, ‘-’, ‘’, ‘/’ operators perform addition, subtraction, multiplication and division respectively on the top two items from the stack. • After processing an input string, the calculator displays the current contents of the stack as a space-separated list. • Numbers should be stored on the stack to at least 15 decimal places of precision, but displayed to 10 decimal places (or less if it causes no loss of precision). • All numbers should be formatted as plain decimal strings (ie. no engineering formatting). • If an operator cannot find a sufficient number of parameters on the stack, a warning is displayed: operator (position: ): insufficient parameters • After displaying the warning, all further processing of the string terminates and the current state of the stack is displayed.