Calculator

Simple calculator in C#.NET used by a windows form and a console application.

Basic Implementation The class implements the following methods: Calculator(left, right, operator)

• Constructor, all three parameters are strings
• valid values for left and right are numbers
• valid values for operator are: "+", "-", "*", "/" setLeft(value)
• assigns the left side of the equation
• value is a string representing a number setRight(value)
• assigns the right side of the equation
• value is a string representing a number setOperator(value)
• assigns the operator
• value is one of: "+", "-", "*", "/" calculate()
• performs the calculation using left, right, and operator getResult()
• returns a string representing the current result
• may return an error message getPreviousResult(index)
• returns a previous result
• index = 1 returns the result immediately prior, index = 2 the one before that, etc
• index is an integer from 1 to 10 Consider various errors that could occur in your implementation, such as:
• left/right/operator parameters are invalid (empty strings, null, letters, etc)
• arithmetic causes an overflow (passing two very large numbers and "+"))- invalid operations (params like left:"1", right:"0", operator:"/") Feel free to implement unit tests if desired. Here are some example parameters and the expected return values from the calculate() method: left:"9", right:"1", operator:"+" returns "10" left:"4", right:"-7", operator:"-" returns "11" left:"8", right:"8", operator:"" returns "64" left:"12", right:"3", operator:"/" returns "4" left:"256", right:"0", operator:"/" returns an error message left:"", right:"423", operator:"+" returns an error message left:"foo", right:"14", operator:"+" returns an error message Errors returned by getResult() are undefined, but should be distinct enough to indicate what happened. An application would use the Calculator class as follows (pseudo-code): myCalc = new Calculator("5", "1", "+") myCalc.calculate() print("5 + 1 = " + myCalc.getResult()) myCalc.setLeft("3") myCalc.setRight("9") myCalc.setOperator("") myCalc.calculate() print("3 * 9 = " + myCalc.getResult()) print("print("previous result: " + myCalc.getPreviousResult(1)) The output from the above program would be: "5 + 1 = 6" "3 * 9 = 27" "previous result: 6"

Part 2: Refactoring The Calculator class is a contrived example, which has a very deliberate API. Implement an alternate class that accomplishes the same goal (simple arithmetic and storing the last 10 results) but with a less verbose API. This second implementation should implement a method that returns the result of a calculation: calculate(equation) Where equation may contain any number of operands and operators. The format of an equation is " ... ", starting and ending with a digit. Support for parentheses is not required. Retain the previous functionality of storing prior results. As with any calculator, it is important that the correct mathematical results are returned. For example, consider the following expression: 10-2*6/4 The correct result is 7