Question

Hello, I'm having trouble with this certain part to a project of mine. Say I have two strings, String left and String right. This is part of an expression evaluation problem, and I need to have a certain piece of the expression in left and a certain piece of the expession in right. The code I have works with everything except if * or / come before + or -. No parentheses included, I have another method that deals with that. Say I have 2+3*3, using my code yoy get 11 which is correct. But if you have 3*3+2, it gives 15 (adding before multiplying). I know why it doesn't work, but I can't seem to fix it, I always end up with a stringoutofbounds exception.

So for example: 2+3*3 String left = 2 String right = 3*3 operation = +

Another example: 8*4-2 String left = 8*4 String right = 2 operation = -

Any help would be greatly apprecited

60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 string left String right char operator float result No parentheses or arrays in mind s. length i++) for int i if (i+1 s length l I i+2 s.length()) f break if (s char t (i-1) l I s charAt (i+1) left s. substring (0, i+1); right s substring (i+2, s. length operator s.charAt (i+1); break else if (s.charAt(i+1) I I S. Char (i+1) left s substring (0, i+1 right s. substring it s length s.charAt it operator break

EDIT: I solved this myself, thanks anyway if anyone was going to help.

Answer 1

Hi Friend, Please find my approach to solve Infix directly if it does not contains brackets.

NOTE: all operators and operands should be separated by a space.

import java.util.Scanner;

public class InfixEvaluation {

   public static double computeInfixExpr(String input) {

       String[] expr = input.split(" ");

       int i = 0;

       double operLeft = Integer.valueOf(expr[i++]);

       while (i < expr.length) {

           String operator = expr[i++];

           double operRight = Double.valueOf(expr[i++]);

           switch (operator) {

           case "*":

               operLeft = operLeft * operRight;

               break;

           case "/":

               operLeft = operLeft / operRight;

               break;

              

           case "+":  

           case "-":

               while (i < expr.length) {

                   String operator2 = expr[i++];

                   if (operator2.equals("+") || operator2.equals("-")) {

                       i--;

                       break;

                   }

                   if (operator2.equals("*")) {

                       operRight = operRight * Double.valueOf(expr[i++]);

                   }

                   if (operator2.equals("/")) {

                       operRight = operRight / Double.valueOf(expr[i++]);

                   }

               }

               if (operator.equals("+")) {

              operLeft = operLeft + operRight;

              }

              else {

              operLeft = operLeft - operRight;

              }

               break;

           }

       }

       return operLeft;

   }

  

   public static void main(String[] args) {

      

       Scanner sc = new Scanner(System.in);

       System.out.println("Enter infix : ");

       String infix = sc.nextLine();

      

       System.out.println(computeInfixExpr(infix));

   }

}

/*

Sample run:

Enter infix :

3 * 3 + 2

11.0

*/