PROJECT 1

CSC172 PROJECT 1

INFIX CALCULATOR

1 Introduction

This project will require you to create a Java program that will take an input file consisting of several

lines of mathematical expressions in infix notation, convert them to postfix notation using the shuntingyard

algorithm, and then evaluate the postfix expression. The results of the calculations will then be

saved to an output file. This project will make use of your Stack and Queue implementations

previously made in lab.

2 Shunting-Yard Algorithm

The first part of the project involves converting infix expressions to postfix using the shunting-yard

algorithm and the stack and queue implementations you wrote in lab 6. You should not use the stack

and queue classes from the Java library. Each infix expression may contain any combination of the

following mathematical operators: addition [+], subtraction [-], multiplication [*], division [/],

parentheses [()], less than [<], greater than [>], equal to [=], logical AND [&], logical OR [|], and

logical NOT [!]. When using the mathematical and logical operators together, let “false” be

represented by 0 and “true” be represented by 1. Extra credit is available for programs that can support

the following additional operators: exponentiation [^], modulo [%], sine [sin], cosine [cos], and tangent

[tan].

The shunting-yard algorithm works by considering each “token” (operand or operator) from an infix

expression and taking the appropriate action:

1. If the token is an operand, enqueue it.

2. If the token is a close-parenthesis [‘)’], pop all the stack elements and enqueue them one by one

until an open-parenthesis [‘(‘] is found.

3. If the token is an operator, pop every token on the stack and enqueue them one by one until you

reach either an operator of lower precedence, or a right-associative operator of equal precedence

(e.g. the logical NOT is a right-associative operator). Enqueue the last operator found, and push

the original operator onto the stack.

4. At the end of the input, pop every token that remains on the stack and add them to the queue

one by one.

The queue now holds the converted postfix expression and can be passed onto the postfix calculator for

evaluation.

3 Postfix Evaluation

With your postfix expression stored in the queue, the next step is to evaluate it. The algorithm for

evaluating a postfix expression proceeds as follows:

1. Get the token at the front of the queue.

2. If the token is an operand, push it onto the stack.

3. If the token is an operator, pop the appropriate number of operands from the stack (e.g. 2

operands for multiplication, 1 for logical NOT). Perform the operation on the popped

operands, and push the resulting value onto the stack.

Repeat steps 1-3 until the queue is empty. When it is, there should be a single value in the stack – that

value is the result of the expression.

4 Deliverable

For this project, you will need to write a Java program that reads in a series of infix expressions from a

plain text file, converts the expressions to postfix notation, evaluates the postfix expressions, and saves

the resulting answers to a new text file. You may assume that the input file will contain valid infix

expressions that can be safely evaluated to numbers (e.g. they won't include division by zero). Extra

credit will be awarded if your program can safely handle invalid input by printing a relevant error

message in the output file.

The file “infix_expr_short.txt” provided with this prompt contains a subset of the expressions the TAs

will use when grading your program. The output of your program should exactly match

“postfix_eval_short.txt” in order to receive full credit. You can check if two files are equivalent by

using the “diff” command on OS X or Linux, or “FC” on Windows. It is strongly recommended that

you write your own (additional) test cases and submit them with your source code to demonstrate your

program's capabilities.

The locations of the input and output files will be supplied to your program via the command line. The

first command line argument will be the location of the input file (containing infix expressions), and

the second argument will be the location where your postfix evaluations should be stored. For example,

if your main method were in a class called InfixCalculator, your program should be run as:

java InfixCalculator infix_expr_short.txt my_eval.txt

5 Hand In

Hand in the source code from this lab at the appropriate location on the Blackboard system at

my.rochester.edu. You should hand in a single compressed/archived (i.e. “zipped” file that contains the

following.)

1. A plain text file named README that includes your contact information, a detailed synopsis of

how your code works and any notable obstacles you overcame, and a list of all files included in

the submission. If you went above and beyond in your implementation and feel that you deserve

extra credit for a feature in your program, be sure to explicitly state what that feature is and why

it deserves extra credit.

2. Source code files (you may decide how many you need) representing the work accomplished in

this project. All source code files should contain author identification in the comments at the top

of the file.

3. A plain text file named OUTPUT that includes author information at the beginning and shows

the compile and run steps of your code. The best way to generate this file is to cut and paste

from the command line.

4. Any additional files containing extra test cases and your program's corresponding output.

Theses cases should be described in your README so the grader knows what you were testing

and what the expected results were.

6 Grading

70% Functionality

10% driver program that handles File I/O

30% infix to postfix conversion according to the shunting-yard algorithm

30% postfix evaluation

20% Testing

15% program passes the short tests

5% program passes the extended tests

10% README

Extra Credit

10% For supporting exponentiation, modulo, sine, cosine, and/or tangent operators (2% each)

10% For gracefully handling invalid expressions and/or expressions that cannot be evaluated

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