Chapter 21, Problem 4PC

Program Plan Intro

Prefix Calculator

Program plan:

• Include necessary header files.
• Define the class “PreficCalc”.
  • Declare the necessary variables.
  • Define the method “start()”.
    • Create labels and text fields to enter the prefix expression.
    • Create a button “evaluate” to submit and calculate the resultant value.
  • Define the class “CmdTextListener”.
    • Define the method “handle()”.
      • Declare the string variable to get a prefix expression.
      • Declare the method “buildExpr()” to read and build a binary tree.
      • Declare the method “eval()” to evaluate the tree expression.
      • Display the result into the resultant text field.
        • Define the method “eval()” to evaluate the expression.
        • • The “if” statement check, left and right child of tree is equal to null.
            • True, return the integer value.
          • Otherwise,
            • Call the method “eval()” and assign the result into “leftOp”.
            • Call the method “eval()” and assign the result into “rightOp”.
            • The “if” statement check, tree value is equal to “*”.
              • True, return the multiplied value.
                • The “if” statement check, tree value is equal to “+”.
                  • True, return the added value.
          • Return “0”.
            • Define the method “isNumber()”.
              • If the given expression is number then, return the number itself.
          • Define the class “Node”.
            • Declare the necessary variables.
            • Define the parameterized constructor.
          • Define the method “buildExpr()” to read and build a binary tree.
            • Read the input from the user.
            • The “if” statement check the expression is number.
              • True, return the node itself.
                • Otherwise, build a non-leaf tree.
                  • Call the method “Node()” and return a value.
  • Define the “main()” method.
    • Declare the method “launch()” to call the “start()” method eventually.