Tutorial: How to Convert Infix to Postfix

HelloWorld · #1 (**permalink**) 08-15-2007, 11:10 PM

Hello everybody,
It's been for a long time that I haven't wrote a tutorial for this website

that's because of my business of real life coding XD lol... Anyways, I hope the code below is self explanatory and may be helpful for you to learn and analyze. Feel free to add some comments, additional ideas or suggestion to improve the code!!!

You are using the code at your own risk! Don't hate me if you got an F or get fired from your work. It's tested and worked at JDK 1.6

Have fun coding!

This is a snippet code that will convert an INFIX expression that's passed through the command line into POSTFIX.

PHP Code:

                  ArrayList<Object> operators = new ArrayList<Object>();
                Stack<Object> checker = new Stack<Object>();
                for (int i = 1; i < args.length; i++) {
                    if (args[i].equals("+")) {
                        if (!checker.isEmpty()) {
                            if (checker.peek().equals("x") || checker.peek().equals("/")) {
                                operators.add(checker.pop());
                                checker.push(args[i]);
                            } else {
                                checker.push(args[i]);
                            }
                        } else {
                            checker.push(args[i]);
                        }
                    } else if (args[i].equals("-")) {
                        if (!checker.isEmpty()) {
                            if (checker.peek().equals("x") || checker.peek().equals("/")) {
                                operators.add(checker.pop());
                                checker.push(args[i]);
                            } else {
                                checker.push(args[i]);
                            }
                        } else {
                            checker.push(args[i]);
                        }
                    } else if (args[i].equals("x")) {
                        if (!checker.isEmpty()) {
                            if (checker.peek().equals("+") || checker.peek().equals("-")) {
                                checker.push(args[i]);
                            } else {
                                operators.add(checker.pop());
                                checker.push(args[i]);
                            }
                        } else {
                            checker.push(args[i]);
                        }
                    } else if (args[i].equals("/")) {
                        if (!checker.isEmpty()) {
                            if (checker.peek().equals("+") || checker.peek().equals("-")) {
                                checker.push(args[i]);
                            } else {
                                operators.add(checker.pop());
                                checker.push(args[i]);
                            }
                        } else {
                            checker.push(args[i]);
                        }
                    } else {
                        operators.add(args[i]);
                    }
                }
                if (!checker.isEmpty()) {
                    for (int i = 0; i <= checker.size(); i++) {
                        operators.add(checker.pop());
                    }
                }

I wanted to say thank you to my graduate friend Steven that helped me found this idea

cheungy · #2 (**permalink**) 11-11-2007, 01:29 AM

which is the String where u take the String and check whether it is a numeric or operator ??

HelloWorld · #3 (**permalink**) 11-11-2007, 08:56 AM

command line argument.. args

cheungy · #4 (**permalink**) 11-12-2007, 12:45 AM

i dont really get it =/ ...

when i make a new string

String TT = "5+5";

and replace everything with args ... it does work

do i need a array for this ?

cuz i dont really get what args stand for

HelloWorld · #5 (**permalink**) 11-12-2007, 10:31 AM

args here means that it's a command line argument, so when you compile your program you pass a command line argument to the program, and that they'll evaluate it that way

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