ECEC301 Assignment - Infix Calculator Assignment - Infix Calculator Introduction This assignment will give you practice with Java, interfaces (not Java interfaces, but the more general notion), and build tools (ant, jar). Write a Java program that will evaluate arithmetic expresions in postfix notation called Calc.java. Expressions in postfix notation contain the operands on which the operation is performed followed by an operator. For example, 3 4 + is equal to 3 + 4 in the infix notation. For this assignment your program should support integer numbers and the following operators: + - * / % (all integer operators). Your interpreter should accept strings of operators and operands seperated by some whitespace from standard input, and print the final result or output an error if the input is invalid. Each line will be a separate expression. EOF is the signal to quit. The Assignment You will write a program that parses infix expressions (described below) into appropriate Tokens (operator or operand), stored in some linear container (ArrayList), passes the infix expression to a function that returns the expression to postfix form, then passes it to a function which evaluates the postfix expression, returns an integer. We'll be doing int arithmetic. Though the inputs are positive, the intermediate results might not be. The operators you will encounter are +, -, *, /, % (modulus). You must also be prepared to handle parenthesis. Your code will be documented properly. Your code I expect to see, at a minimum, 2 methods: infix2postfix evalPostfix I've written Token classes for you (the files are in the class Assignments/Calc directory). You do need to fill in the Operator.getPrec() method, assign appropriate (relative) precedences to the operators. The 2 types, Operand and Operator share a base class, Token, so that you can store an entire expression, in a generic ArrayList which holds Tokens. We need to get used to generics. Sample.java, in the directory, shows the creation and storage of various Tokens in a generic collection. opType is an example of how we did "enums" pre- Java 1.5. Note that you can make these types smarter by assigning precedence right there. You're welcome to make this modification. Yes, you need to use my Token classes. Input Your program will read a file called input.infix that contains a number of expressions, one per line. Each line has, at most, 80 characters. Tokens will be separated by white space. Operands will be strictly non-negative integers. Operators are: { + - * / % } for addition, subtraction, multiplication, division, and modulus, respectively. Here is a sample input: 13 + 23 - 42 * 2
3 * ( 5 - 2 ) % 5 A sample input file can be found here. For my part, I promise that all expressions are valid. Output Your program will output, for each input expression, on one line: postfix expression = result , where result is the value of expression. There will be one expression per line (same as the input). Single-space only, please. So, given the input, above, I'd expect the output to be: 13 23 + 42 2 * - = -48
3 5 2 - * 5 % = 4 Documentation I am NOT looking for a lot of comments here. Remember, your code should read like a book. But, each class should have a description, and each method should have a description and a discussion of inputs, side-effects, etc. You will use Javadoc-style comments. HTML documentation will be created from your code, using ant (and javadoc, of course). Algorithms Infix to Postfix Append a right paren ')' to the end of the input expression. Push a left paren '(' onto the stack. Start at the first token. For each token: If it is a left paren, push it onto the stack. If it is a right paren, pop operators from the stack and append to the postfix expression, until a left paren is encountered on the stack. Remove and discard the left paren. If it is an operand, append it to the postfix expression. If it is an operator, then pop operators from the stack and append to the postfix expression while the operators have equal or higher precedence than the current token. Push current token (operator) onto the stack. Remember, we're not treating the parentheses as operators, they're being handled separately. Continue until you've reached the end of the expression. If the input expression was valid, then evey pop() should've been fine, and the stack should be empty. Evaluating Postfix Expressions Start at the first token. For each token: If it is an operand, push it on the stack. Else if it is an operator, then y ← pop top value x ← pop top value result ← x (oper) y push result onto stack fi Continue until you've reached the end of the expression. There should be exactly one element in the stack; the result of the expression. The main function will parse the input file and hand the expressions to this function to evaluate. See the StreamTokenizer examples. Or, since the Java community is moving away from this, you might look at the String.split methods. Files for Download Operator.java Operand.java opType.java Token.java Sample.java Submission Calc.java - Your driver, container for static methods, post2infix, etc. Operator.java - You need to fill the in the getPrec method of my file, submit it Any other source files you need. .class files will be deleted before I start, so, must be built from source. README optional - Anything you want to tell me before I grade If you supply input.infix it will be overwritten. Please note You will use the filenames as listed here, and submit them all to the proper assignment. If this is not clear, then see me in class. If I get programs submitted to the wrong directories, I will be irate, which may, in some subconscious way, affect your grades. Adversely.
