Question

Question: Write a Java program for Evaluating Postfix Expression 1. Input a postfix expression from user. 2. Evaluate expression using double stack made of your own linked list. 3. Show the result of expression or error if incorrect. Evaluating Postfix Expression Input an expression: 2 10 + 9 6 - / Evaluating Postfix Expression Input an expression: 20 10 + 9 6 - 1 Evaluating Postfix Expression Input an expression: 2 10 + 9 - / Result = 4.0 Result = 4.0 Result = Error Note : • Input expression will be a String. After the input, parse the string for numbers and operators. Operands may be integers, and floats or doubles. Hence use a stack which can store doubles.

Answer 1

3 public class StackMethods { public class node /node class double data; node next; OOOHN node top=null; public void push (double d) //push mwthod node newnode=new node(); newnode.data=d; newnode.next=null; if(top==null) top=newnode; else newnode.next=top; top=newnode; OOHNMOOOH public double pop() //pop method double temp=top.data; top=top.next; return temp;

3 public class mainClass2 { static double evaluate Postfix (String exp) Ocon WN //create a stack StackMethods stack = new StackMethods(); // Scan all characters one by one for (int i = 0; i < exp.length(); i++) char c = exp.charAt(i); if (c == '') continue; // If the scanned character is an operand // (number here), extract the number // Push it to the stack. else if (Character.isDigit(c)) icon WNPoocan int n = 0; //extract the characters and store it in num while (Character.isDigit(c)) n = n*10 + i++; (int) (c-'0');

i--; //push the number in stack stack.push(n): // If the scanned character is an operator, pop two // elements from stack apply the operator else double vall = stack.pop(); double val2 = stack.pop(); switch(c) case !+!: stack.push(val2+vall); break; case '-': stack.push(val2- vall); break; case '/' : stack.push (val2/vall); break; case :

case 1: stack.push(val2*vall); break; return stack.pop(); public static void main(String[] args) String exp = "2 10 + 9 6 - /"; System.out.println("Result : "+evaluate Postfix (exp));

Il Problems @ Javadoc . Declaration Console <terminated> mainClass2 [Java Application) C:\Program Fil Result : 4.0

source code:

package preparation;

public class StackMethods {

   public class node //node class
   {
       double data;
       node next;
   }
  
node top=null;
  
   public void push(double d)
   { //push mwthod
       node newnode=new node();
       newnode.data=d;
       newnode.next=null;
       if(top==null)
           top=newnode;
       else
       {
           newnode.next=top;
       top=newnode;
       }
      
   }
   public double pop()
   {
       double temp=top.data; //pop method
       top=top.next;
       return temp;
      
   }
}

package preparation;

public class mainClass2 {
  
   static double evaluatePostfix(String exp)
{
//create a stack
StackMethods stack = new StackMethods();
  
// Scan all characters one by one
for(int i = 0; i < exp.length(); i++)
{
char c = exp.charAt(i);
  
if(c == ' ')
continue;
  
// If the scanned character is an operand
// (number here),extract the number
// Push it to the stack.
else if(Character.isDigit(c))
{
int n = 0;
  
//extract the characters and store it in num
while(Character.isDigit(c))
{
n = n*10 + (int)(c-'0');
i++;
c = exp.charAt(i);
}
i--;
  
//push the number in stack
stack.push(n);
}
  
// If the scanned character is an operator, pop two
// elements from stack apply the operator
else
{
double val1 = stack.pop();
double val2 = stack.pop();
  
switch(c)
{
case '+':
stack.push(val2+val1);
break;
  
case '-':
stack.push(val2- val1);
break;
  
case '/':
stack.push(val2/val1);
break;
  
case '*':
stack.push(val2*val1);
break;
}
}
}
return stack.pop();
}
  
  
   public static void main(String[] args)
{
String exp = "2 10 + 9 - /";
System.out.println("Result : "+evaluatePostfix(exp));
}

}

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