POSTFIX EXPRESSION EVALUATION

JAVA PROGRAM TO EVALUATE A POSTFIX EXPRESSION USING STACK.

COMPUTER GENERATED OUTPUT IS:

CODING:

import java.io.*;

class postfix

{ int A[];int top,size;

postfix(int n)

{top=-1;A=new int[n];size=n;

}

void push(int ch)

{ if(top==size-1)

System.out.println("Overflow");

else

{top++;A[top]=ch;

}

}

int pop()

{ if(top==-1)

return(-99999);int ch=A[top];

if(top==size-1)

top=-1;

else

top--;

return(ch);

}

public static void main(String args[])throws IOException

{

BufferedReader br=new BufferedReader(new InputStreamReader(System.in));

System.out.println("Enter the post fix expression");

String s=br.readLine();postfix ob=new postfix(s.length());

System.out.println("Enter values Of\t:");

for(int i=0;i<s.length();i++)

{ char ch=s.charAt(i);

if(ch!='*'&&ch!='^'&&ch!='+'&&ch!='-'&&ch!='/')

{System.out.print("\n\t\t"+ch+"\t=\t");

ob.push(Integer.parseInt(br.readLine()));

}

else

{int ans=0; int a=ob.pop(),b=ob.pop();

if(a==-99999||b==-99999)

{System.out.println("Invalid postfix expression");

System.exit(0);

}

if(ch=='+')

ans=a+b;

if(ch=='-')

ans=b-a;

if(ch=='/')

ans=b/a;

if(ch=='*')

ans=b*a;

if(ch=='^')

ans=(int)Math.pow(b,a);

ob.push(ans);

}

}

int ans=ob.pop(); if(ob.pop()==-99999) System.out.println("\t\tAnswer\t=\t"+ans); else System.out.println("\t\tINVALID POSTFIX EXPRESSION"); }

}

}