Calculator

Andrew Braunstein

Single view calculator app for CIS 195

Functionality

Behavior

Once an expression is evaluated, the response is shown in the echo area. Upon pushing any other button, the echo area will clear automatically.

If the first button you push is an operator (+, x, -, ^, ÷), the first argument will be the last answer. The last answer defaults to 0.

If there are two values next to each other, there is implicit multiplication. For example, 4π will be expanded to 4 x π before evaluation. Multiplication is also implicit with parentheses. For example, 4(3 + 2) will be the same as 4 x (3 + 2). This works on the other side of the parentheses as well.

Division by 0 results in Inf, except when we divide 0 by 0 (here the answer is nan). We can still operate on Inf and nan as if they are numbers. If the answer is still computable, then you will get a real number, otherwise, the app will return nan.

Errors

All errors will write to the echo area and will be cleared upon pressing any button.

Errors:

• Mismatched Parentheses
• Illegal number
  • Any number that is poorly formatted, either due to decimal points or negative signs.
• Incorrect number of arguments to this operator
  • If an operator is used incorrectly
• Values left on the stack
  • This may be an error attributed to incorrect use of operators, but will most likely never be thrown

Interesting Buttons

(-) is negation

^ is exponentiation

c is clear

Design

• Input/Output
  • Keyboard
    • keypad with numbers and operators
    • second keypad with symbols and advanced functions (pi, e, sqrt, etc.)
    • Submit key
  • Echo area
    • Shows a representation of what has been typed by the user
    • Once the user hits submit, this will show the output
• Math
  • All math is floating point
  • If int(x) = float(x), show as an int, otherwise show with 3 decimal places
  • Order of operations will be done with a binding value and how it associates (left or right)
  • The data will be computed on in a tree like manner recursively by applying the operator at the node of the tree to the left and right children.
• Parser
  • Maybe use ParseKit
  • Possibly just hand roll it
• Classes
  • Echo area - Deals with showing the user either what they have typed or what was computed
  • Parser - Parses the text into a tree like data structure that can then be evaluated by the calculator
  • Calculator - Deals with the computations and the current calculator state (history, last equation, constants, etc.)