"Calculator" "Not a number" "Error" "." "0" "1" "2" "3" "4" "5" "6" "7" "8" "9" "cos" "ln" "log" "sin" "tan" "clr" "del" "Euler\'s number" "pi" "point" "left parenthesis" "right parenthesis" "cosine" "natural logarithm" "logarithm" "sine" "tangent" "plus" "divide" "factorial" "times" "power" "square root" "minus" "clear" "delete" "equals"