/**
 * Informatik II - FS2009 <br>
 * Uebungsserie 4, Aufgabe 1 <br>
 *
 * The class InfToPost allows to convert infix expressions
 * to postfix expressions. <br>
 * See also lecture script: "Postfixumwandlung mittels Stack" (Folie 138) <br>
 *
 * @author Philipp Bolliger <br>
 **/

public class InfToPost {

    Stack stack = new Stack(); // Create a stack with 100 elements

    /**
     * Outputs the content of the input-array in
     * postfix notation
     *
     * @param input ...ADD YOUR COMMENTS HERE...
     **/
    public void convert(char[] input) {
        int i = 0;

        while( i < input.length ) {

            //push operands on stack
            if(input[i] == '+' || input[i] == '*') {
                stack.push( input[i] );
            }

            // From http://java.sun.com/j2se/1.4.2/docs/api/:
            //
            // "The Character class wraps a value of the primitive type
            // char in an object. An object of type Character contains
            // a single field whose type is char. In addition, the
            // Character class provides several methods for determining
            // a character's category (lowercase letter, digit, etc.)
            // and for converting characters from uppercase to lowercase
            // and vice versa."
            //
            // isDigit( char c ) is a method of the Character class, which
            // for a character c ascertains whether c is a digit or not.
            // The same functionality may be obtained through the
            // expression: "(c >= '0' && c <= '9')"

            //print digit
            if( Character.isDigit( input[i] ) ) {
                System.out.print( " " + input[i] );
            }

            //print operand
            if( input[i] == ')' ) {
                System.out.print( " " + (char)stack.pop() );
            }

            i++;
        } // end while()

        System.out.println();

        // Think about...
        // The following check may detect a syntax error!
        if( ! stack.empty() ) {
            System.out.println( "Error: uncorrect expression" );
        }
    }

    /**
     * Test inputs:
     *      ((5+13)*((23+17)*81))
     *      (12+(5*((76+42)+19)))
     **/
    public static void main(String[] args) {

        if( args.length == 0 ||  args.length > 1 ) {
            System.out.print("Invalid Input!");
            System.out.println(" Please enter an infix expression" +
            " as one-string argument.");
            System.out.println("Example: java InfToPost \"((7+5)*9)\"" );
            System.exit( 1 );
        }

        //convert input string in a char array
        char[] input = args[0].toCharArray();
        InfToPost expression = new InfToPost();

        //Convert and print coverted expression
        expression.convert(input);
    }
}