iPhone Development CIS 195 Project 1 Sebastian Schloesser
APP INSTRUCTIONS
Guide to use calculator app.
Buttons: left arrow - decoration
right arrow - decoration
orange alt button - alt option
clear - backspace, clears all when alt is selected
+/- - if there is only one number on the screen, it will invert its sign
X - variable x
STR - computes whatever is on the screen and stores it as variable X
pi - insert pi constant, e constant when alt is selected
ENTER - compute expression on screen
Everything else is self explanatory.
INITIAL PLAN
This project will consist of creating an iOS calculator. In order to follow a proper MVC structure, I will place all the computation methods in a model class. The view will be all held in the storyboard and its respective controller will be in the ViewController class. After I finish designing a UI that satisfies all the project requirements, such the arithmetic operations, a number pad, a decimal point, etc. I will wire all the buttons to the controller. Buttons will place a string on the calculator's "screen". Rather than operating like most calculators, where one can only do one operation at a time, I plan on allowing the user to create a string of operations on the string that will then be executed, just like in scientific/graphing calculators. This means that when the user hits enter, an NSString will be sent to the model for parsing. Then, I will need to determine the order of operations and place the operands and operators in data structures in the right order. Finally, they will be executed in an RPN fashion and then the result will be sent back to the screen. If the string does not make sense or contains a division by zero, an error message can be sent to the screen. All numbers will be contained in floats.
The model would contain a method called compute, which takes a string and returns a float. This method would then call a method that parses the string and returns a data structure with all the operators and another one with all the operands in order. Then I will iterate through the operators looking for them in the proper order. For example, if I had the string "1+3*7", I would get operators = [+, *] and operands = [1, 3, 7]. I would first look for multiplications, so I would get that operators(1) is a multiplication so I would perform the operation operands(1)*operands(2), delete both those entries from the structure and put the result back at operands(1). This process could continue to complete the operation of the entire string.
In the future, I could add exponent and parenthesis capabilities by improving the parsing system. I could write another method that gets the string first and separates each parenthesis into a string of its own that gets computed and then placed back on the original one so that the same methods described above can solve the entire thing.
To ensure that the string is valid, intelligence needs to be added to the ViewController. This means that the user won't be able to place two operators next to each other and other things that don't make sense, such as just placing a decimal point for an operand, etc.