Question

Write a java program for the following:

Your program reads an infix expression represented by a string S from the standard input (the keyboard). Then your program converts the infix expression into a postfix expression P using the algorithm. Next, your program evaluates the postfix expression P to produce a single result R. At last, your program displays the original infix expression S, the corresponding postfix expression P and the final result R on the standard output ( the screen ). Your program is required to handle at least five mathematic operations, +, -, * and /, and ^(exponential). When you perform division, please do integer division. For example, 7 / 2 is 3. Note that in this program, the input infix expression contains one-digit operands and produces one-digit result. In other words, you do not worry about the infix expressions that involve multiple-digit operands and produce multiple-digit results.

Note that you have to implement your own Stack class in this program. The built-in Java Stack is not allowed in this program.

Please use Java Object type or the generic type E for the data element in your stack implementation. Please catch any potential errors, so that your program will not crash. You do not need to check whether all parentheses in the input infix expression are correctly matched or not. You can safely assume the format of the infix expression is correct. Each run of your program will evaluate only one infix expression.

Sample Run One

Please enter the infix expression to process: (((1+2)-(3-4))/(6-5))

The postfix expression for the input infix is: 1 2 + 3 4 - - 6 5 - /

The final result after evaluating the postfix is: 4

Sample Run Two

Please enter the infix expression to process: 2 * 4 - 2 ^ 2 ^ 1

The postfix expression for the input infix is: 2 4 * 2 2 1 ^ ^ -

The final result after evaluating the postfix is: 4

Answer 1

//Java program

import java.util.Stack;
import java.util.Scanner;
public class InfixtoPostfix {
     
public static void main(String[] args)
{
String expression;
Scanner in = new Scanner(System.in);
System.out.print("Please enter the infix expression to process:");
expression = in.nextLine();
String postfix = infixToPostfix(expression);
System.out.println("The postfix expression for the input infix is:"+postfix);
System.out.println("The final result after evaluating the postfix is:"+evaluatePostfix(postfix));
in.close();
}
  

public static String infixToPostfix(String exp)
   {
   String result = new String("");
  
   Stack<Character> stack = new Stack<>();
  
   for (int i = 0; i<exp.length(); ++i)
   {
   char c = exp.charAt(i);
   if(c==' ')continue;
   if (Character.isLetterOrDigit(c))
   result += c;
  
   else if (c == '(')
   stack.push(c);
  
   else if (c == ')')
   {
   while (!stack.isEmpty() && stack.peek() != '(')
   result += stack.pop();
  
   if (!stack.isEmpty() && stack.peek() != '(')
   return "Invalid Expression"; // invalid expression   
   else
   stack.pop();
   }
   else // an operator is encountered
   {
   while (!stack.isEmpty() && Prefer(c) <= Prefer(stack.peek()))
   result += stack.pop();
   stack.push(c);
   }
     
   }
     
   // pop all the operators from the stack
   while (!stack.isEmpty())
   result += stack.pop();
     
   return result;
   }
public static int Prefer(char ch)
{
switch (ch)
{
case '+':
case '-':
return 1;
  
case '*':
case '/':
return 2;
  
case '^':
return 3;
}
return -1;
}   
  
     
   public static int evaluatePostfix(String expression)
   {
   Stack<Integer> stack=new Stack<>();
  
   for(int i=0;i<expression.length();i++)
   {
   char c=expression.charAt(i);
  
   if(Character.isDigit(c)) {
         
   stack.push(c-'0'); }
     
   else
   {
   int val1 = stack.pop();
   int 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;
  
   case '^':
       stack.push((int)Math.pow(val2, val1));
       break;
   }
   }
   }
   return stack.pop();   
   }
}
//sample output

<terminated> InfixtoPostfix [Java Application] CAProgram FilesJavaljdk1.8.0_151\bin avaw.exe Please enter the infix expression to process: 2*4 221 The postfix expression for the input infix is:24*221 The final result after evaluating the postfix is:4

sterminated> InfixtoPostfix [Java Application] C:AProgram FilesJavajdk1.8.0_151\binjavaw.exe (Feb 25 Please enter the infix expression to process: ( (1+2) (3-4))/(6-5)) The postfix expression for the input infix is: 12+34--65- The final result after evaluating the postfix is:4