Postfix Expressions Problem
I wrote a program for my AP Comp Sci A class that takes a postfix expression (e.g. 32+) and converts it into an infix expression (e.g. 3+2) and then solves it. It worked before I converted it into the 'solve' method, but now I did (because its required), it keeps giving me an EmptyStackException on the line "if(comparingyay.compareTo("+")==0)
stk.push(stk.pop()+stk.pop());
"
If anyone can help me debug this, I would be forever greatful.
import java.util.*;
import java.io.*;
publicclass PostfixExpressions
{
publicstaticvoid main(String[] args)
{
Scanner scan=new Scanner(System.in);
String in=scan.next();
int answer=solve(in);
System.out.println(answer);
}
publicstaticint solve(String y)
{
Stack<Integer> stk=new Stack<Integer>();
for(int x=0;x<y.length();x++)
{
char chars1=y.charAt(x);
if(Character.isLetterOrDigit(chars1))
{
Integer ints=new Integer(0);
stk.push(ints.valueOf(y.substring(x,x+1)));
}
String comparingyay=y.substring(x,x+1);
if(comparingyay.compareTo("+")==0||comparingyay.compareTo("-")==0||
comparingyay.compareTo("*")==0||comparingyay.compareTo("/")==0)
{
if(!stk.isEmpty())
{
if(comparingyay.compareTo("+")==0)
stk.push(stk.pop()+stk.pop());
elseif(comparingyay.compareTo("-")==0)
{
int b=stk.pop();
int a=stk.pop();
stk.push(a-b);
}
elseif(comparingyay.compareTo("/")==0)
{
int b=stk.pop();
int a=stk.pop();
stk.push(a/b);
}
elseif(comparingyay.compareTo("*")==0)
stk.push(stk.pop()*stk.pop());
}
}
}
return stk.pop();
}
}
>
