Can anyone spot the problem?

Question

Hey i've been workin on an applet which accepts two boolean equations with 3 variables and returns an answer telling if they are logically equal. When it comes to the PLUS and MINUS cases the program works fine. However in the TIMES and DIVIDE cases it returns at least one wrong answer, despite the fact i'm using the logical AND gate. For example if i enter x*y the program returns
answer 1 = O, when (x,y)=(0,0)
answer 2 = 1, when (x,y)=(1,0)
answer 3 = O, when (x,y)=(0,1)
answer 4 = 1, when (x,y)=(1,1)
were answer 2 is wrong using an AND gate.
Here is the for loop which passes the values
             for (int y = 0; y < 2; y++)
               for (int x = 0; x < 2; x++)
                   int d = MyParser.answer(x, y);
                   int doub = MyParser2.answer(x, y);
                   String eq = "";
                   if (d == doub) {
                     equal++;
                     count++;
                     eq = "equal\t";
                   else {
                     count++;
                     eq = "not equal";
                   tb1.append("\nAnswer was " + d + "\t " + eq + " " +
                              "\t answer 2 was " + doub);
               }and here is the code for the parser
package Applet1;
public final class Parse
  public Parse (String equation)
    parse (equation);
   public int answer(int x,int y, int z)
     return this.value(x,y,z);
   public int answer(int x,int y)
     return this.value(x, y);
   public int answer(int x)
     return this.value(x);
   public int value(int x)
     return val(x, 0, 0);
   public int value(int x, int y)
     return val(x, y, 0);
   public int value(int x, int y, int z)
     return val(x, y, z);
   public String getEquation()
    return equation;
  private String equation;
  private byte[] code;
  private int[] stack;
  private int[] constant;
  private int pos = 0, constantCt = 0, codeSize = 0;
  private static final byte
  PLUS = -1,   MINUS = -2,   TIMES = -3,   DIVIDE = -4,
  UNARYMINUS = -5, VARIABLEX = -6, VARIABLEY = -7, VARIABLEZ = -8;
  private char next()
    if (pos >= equation.length())
    return 0;
    else
    return equation.charAt(pos);
  private void skip()
    while (Character.isWhitespace(next()))
    pos++;
  private int val(int variableX, int variableY, int variableZ)
   try
     int top = 0;
     for (int i=0; i < codeSize; i++)
       if (code[i] >= 0)
         stack [top++] = constant [code ];
else if (code [i] >= UNARYMINUS)
int y = stack[--top];
int x = stack[--top];
int w;
int ans = (int) Double.NaN;
switch (code[i])
case PLUS: ans = x | y;
break;
case MINUS: ans = (x) & (~y);
break;
case TIMES: ans = x & y;
break;
case DIVIDE: ans = x & ~y;
break;
if (Double.isNaN(ans))
return ans;
stack [top++] = ans;
else if (code[i] == VARIABLEX)
stack [top++] = variableX;
else if (code[i] == VARIABLEY)
stack [top++] = variableY;
else if (code[i] == VARIABLEZ)
stack [top++] = variableZ;
catch (Exception e)
double b = Double.NaN;
int i = (int) b;
return i;
double d2;
if (Double.isInfinite(stack[0]))
d2 = Double.NaN;
int i2 = (int) d2;
return i2;
}else
return stack[0];
private void error (String message)
throw new IllegalArgumentException
("Parse error: " + message + "\n");
private int stackUse()
int s = 0;
int max = 0;
for (int i = 0; i < codeSize; i++)
if (code[i] >= 0 || code [i] == VARIABLEX || code[i] == VARIABLEY || code[i] == VARIABLEZ)
s++;
if (s > max)
max = s;
} else if (code[i] >= UNARYMINUS)
s--;
return max;
private void parse (String equation)
if (equation == null || equation.trim().equals(""))
error ("No Data to be parsed");
this.equation = equation;
code = new byte[equation.length()];
constant = new int [equation.length()];
parseExpress();
skip();
int stackSize = stackUse();
stack = new int[stackSize];
byte[] c = new byte[codeSize];
System.arraycopy(code,0,c,0,codeSize);
code = c;
int[] A = new int[constantCt];
System.arraycopy(constant,0,A,0,constantCt);
constant = A;
private void parseExpress()
boolean neg = false;
skip();
parseVaries();
if (neg)
code[codeSize++] = UNARYMINUS;
skip();
while (next() == '+' || next() == '-')
char op = next();
pos++;
parseTerm();
if (op =='+')
code[codeSize++] = PLUS;
else
code[codeSize++] = MINUS;
skip();
private void parseTerm()
parseFactor();
skip();
while (next() == '*' || next() == '/')
char op = next();
pos++;
parseFactor();
code[codeSize++] = (op == '*')? PLUS:MINUS;
skip();
private void parseFactor()
parseVaries();
skip();
while (next() == '^')
pos++;
parseVaries();
code[codeSize++] = UNARYMINUS;
skip();
private void parseVaries()
skip();
char ch = next();
if (ch == 'x' || ch =='X')
pos++;
code[codeSize++] = VARIABLEX;
else if (ch == 'y' || ch == 'Y')
pos++;
code[codeSize++] = VARIABLEY;
else if (ch == 'z' || ch == 'Z')
pos++;
code[codeSize++] = VARIABLEZ;
else if (ch == '(')
pos++;
parseExpress();
skip();
if (next () !=')')
error("Right parenthesis needed");
pos++;
else if (ch == ')')
error ("Need a left parenthesis");
else if (ch == '+' || ch == '-' || ch == '*' || ch =='/' || ch =='^')
error ("Operator" + ch + "\n found in unexpected position");
else if (ch == 0)
error ("Incorrect entry");
else
error ("Illegal character " + ch);
Its not pretty i know and its missing a part to parse Digits and i'm using type casting for strange reasons, but it does work. Except for in these two cases, can anyone see why
Thanks
podger

Answer 1

I'm not even entirely certain what you are trying to accomplish here.
It looks wrong in any case.
I can't see anything in the way of debugging, so heres my help for today:
public void printCode(){
      System.out.println(equation + ":");
      for(int i=0; i<code.length; i++){
        switch(code){
case PLUS: System.out.print("Plus "); break;
case MINUS: System.out.print("Minus "); break;
case TIMES: System.out.print("TIMES "); break;
case DIVIDE: System.out.print("DIVIDE "); break;
case UNARYMINUS: System.out.print("-"); break;
case VARIABLEX: System.out.print("x "); break;
case VARIABLEY: System.out.print("y ");break;
case VARIABLEZ:System.out.print("z ");break;
System.out.println();
I suggest you parse a couple of expressions, and print out the code generated using this handy little method.
Parse parse = new Parse("x+y");
parse.printCode();       
parse = new Parse("x*y");
parse.printCode();(x+y) : x y Plus
(x*y) : x
I think you will find the problem in your parseExpress method (well one of your problems anyway)
Also take a look at your ParseTerm function - I'm pretty sure that a * is meant to represent "TIMES" and not "PLUS"
Did you ever thing about using switch statements rather than ifs?
Good luck,
evnafets