Error In EVALUATE POSTFIX program (Program Getting Compiled)

[red_ferrari007]

PROGRAM GETS COMPILED...BUT GIVES ERROR ARRAY OUT OF BOUNDS...PLEASE HELP AS SOON AS POSSIBLE !!!

import java.io.*;
class Evaluate
{
char postfix[];
int stack[];
int i,a,b,c,top,n;
BufferedReader input=new BufferedReader(new InputStreamReader(System.in));
Evaluate() throws IOException
{
System.out.println("ENTER ARRAY SIZE");
n=Integer.parseInt(input.readLine());
postfix=new char[n];
stack=new int[n];
top=-1;
i=-1;
}

void readpostfix() throws IOException
{
char p;
System.out.println("ENTER STRING");
do
{
p=(char)input.read();
i++;
postfix[i]=p;
}
while(p!='\n');
postfix[i]='\0';
}

boolean isoperand(char c)
{
if(c>='0'&&(c<='9'))

return true;
else
return false;
}

void compute()
{
for(i=0;postfix[i]!='\0';i++)
if(isoperand(postfix[i]))
{
top++;
stack [top]= (int) (postfix[i]-'0');
}
else
{
a=stack[top];
top--;
b=stack[top];

switch(postfix[i])
{
case'+':c=b+a;
stack[top]=c;
break;
case'-':c=b-a;
stack[top]=c;
break;

case'*':c=b*a;
stack[top]=c;
break;
case'/':c=b/a;
stack[top]=c;
break;

default:System.out.println("INVALID OPERATOR");
}
}

System.out.println("THE VALUE OF POSTFIX EXPRESSION IS "+stack[top]);
}

public static void main(String args[])throws IOException
{
Evaluate e=new Evaluate();
e.readpostfix();
e.compute();
}
}

[NormR1]

Please edit your post, select the code and wrap it in code tags. Use the [CODE] icon above the input box.

You forgot to post the full text of the error message so we could see where it occurred and what the value of the index was.