Binary Cipher
//Evaluating the postfix expression
import java.util.*;
class postfix1
{
double a[]=new double[20];
int top;
postfix1() { top=-1; }
void push(double x)
{
top++;
a[top]=x;
}
double pop()
{
if(top==-1) { System.out.println(“nImproper expression !”+(char)7); System.exit(1); }
return a[top–];
}
boolean isdigit(char x)
{
return(x>=’0′ & x<=’9′);
}
double val(double v1,double v2,char x)
{
switch(x)
{
case ‘+’: return v1+v2;
case ‘-‘: return v1-v2;
case ‘*’: return v1*v2;
case ‘/’: return v1/v2;
case ‘$’: return (Math.pow(v1,v2));
default : System.out.println(“Improper Operation”);
System.exit(1);
}
return 1;
}
double eval(char b[])
{
double v1,v2,v3,v;
for(int i=0;i<b.length;i++)
{
if(isdigit(b[i]))
push((double)b[i]-48);
else
{
v2=pop();
v1=pop();
v=val(v1,v2,b[i]);
push(v);
}
}
if(top!=0) { System.out.println(“nImproper expression”+(char)7); System.exit(1); }
return pop();
}
}
class Postfix
{
public static void main(String args[])
{
postfix1 p=new postfix1();
Scanner scr=new Scanner(System.in);
System.out.println(“nEnter the post fix expression : “);
String str=scr.next();
char b[]=str.toCharArray();
System.out.print(“nValue of the expression is : “+p.eval(b));
}
}
Output:
Enter the postfix expression :
23+43+-
Value of the expression is : -2.0