Java.. I understand how to get the user input.. I need to add the \"^\" and \"%\

Question

Java.. I understand how to get the user input.. I need to add the "^" and "%"

(Evaluate expression) Modify Listing 20.9 EvaluateExpression.java to add
operators ^ for exponent and % for modulus. For example, 3 ^ 2 is 9 and 3 % 2
is 1. The ^ operator has the highest precedence and the % operator has the same
precedence as the * and / operators. Your program should prompt the user to
enter an expression.

Here is a sample run of the program:
Enter an expression: (5 * 2 ^ 3 + 2 * 3 % 2) * 4
(5 * 2 ^ 3 + 2 * 3 % 2) * 4 = 160

Listing 20.9
import java.util.Stack;
import java.util.Scanner;

public class Beginning {
public static void main(String[] args) {
// Check number of arguments passed
      String[] go = {"(5+32)*4"};
if (go.length != 1) {
System.out.println(
"Usage: java EvaluateExpression "expression"");
System.exit(1);
}

try {
System.out.println(evaluateExpression(go[0]));
}
catch (Exception ex) {
System.out.println("Wrong expression: " + go[0]);
}
}

/** Evaluate an expression */
public static int evaluateExpression(String expression) {
// Create operandStack to store operands
Stack<Integer> operandStack = new Stack<>();

// Create operatorStack to store operators
Stack<Character> operatorStack = new Stack<>();

// Insert blanks around (, ), +, -, /, and *
expression = insertBlanks(expression);

// Extract operands and operators
String[] tokens = expression.split(" ");

// Phase 1: Scan tokens
for (String token: tokens) {
if (token.length() == 0) // Blank space
continue; // Back to the while loop to extract the next token
else if (token.charAt(0) == '+' || token.charAt(0) == '-') {
// Process all +, -, *, / in the top of the operator stack
while (!operatorStack.isEmpty() &&
(operatorStack.peek() == '+' ||
operatorStack.peek() == '-' ||
operatorStack.peek() == '*' ||
operatorStack.peek() == '/')) {
processAnOperator(operandStack, operatorStack);
}

// Push the + or - operator into the operator stack
operatorStack.push(token.charAt(0));
}
else if (token.charAt(0) == '*' || token.charAt(0) == '/') {
// Process all *, / in the top of the operator stack
while (!operatorStack.isEmpty() &&
(operatorStack.peek() == '*' ||
operatorStack.peek() == '/')) {
processAnOperator(operandStack, operatorStack);
}

   // Push the * or / operator into the operator stack
   operatorStack.push(token.charAt(0));
   }
   else if (token.trim().charAt(0) == '(') {
   operatorStack.push('('); // Push '(' to stack
   }
   else if (token.trim().charAt(0) == ')') {
   // Process all the operators in the stack until seeing '('
   while (operatorStack.peek() != '(') {
   processAnOperator(operandStack, operatorStack);
   }

   operatorStack.pop(); // Pop the '(' symbol from the stack
   }
   else { // An operand scanned
   // Push an operand to the stack
   operandStack.push(new Integer(token));
   }
   }

   // Phase 2: Process all the remaining operators in the stack
   while (!operatorStack.isEmpty()) {
   processAnOperator(operandStack, operatorStack);
   }

   // Return the result
   return operandStack.pop();
   }

   /** Process one operator: Take an operator from operatorStack and
   * apply it on the operands in the operandStack */
   public static void processAnOperator(
   Stack<Integer> operandStack, Stack<Character> operatorStack) {
   char op = operatorStack.pop();
   int op1 = operandStack.pop();
   int op2 = operandStack.pop();
   if (op == '+')
   operandStack.push(op2 + op1);
   else if (op == '-')
   operandStack.push(op2 - op1);
   else if (op == '*')
operandStack.push(op2 * op1);
else if (op == '/')
operandStack.push(op2 / op1);
}

public static String insertBlanks(String s) {
String result = "";

for (int i = 0; i < s.length(); i++) {
if (s.charAt(i) == '(' || s.charAt(i) == ')' ||
s.charAt(i) == '+' || s.charAt(i) == '-' ||
s.charAt(i) == '*' || s.charAt(i) == '/')
result += " " + s.charAt(i) + " ";
else
result += s.charAt(i);
}

return result;
}
}

Explanation / Answer

public class Exercise_23 { public static void main(String[] args) { // Check number of arguments passed if (args.length != 1) { System.out.println( "Usage: java EvaluateExpression "expression""); System.exit(1); } try { System.out.println(args[0] + " = " + evaluateExpression(args[0])); } catch (Exception ex) { System.out.println("Wrong expression: " + args[0]); } } /** Evaluate an expression */ public static int evaluateExpression(String expression) { // Create operandStack to store operands Stack operandStack = new Stack(); // Create operatorStack to store operators Stack operatorStack = new Stack(); // Insert blanks around (, ), +, -, /, and * expression = insertBlanks(expression); // Extract operands and operators String[] tokens = expression.split(" "); // Phase 1: Scan tokens for (String token: tokens) { if (token.length() == 0) // Blank space continue; // Back to the while loop to extract the next token else if (token.charAt(0) == '+' || token.charAt(0) == '-') { // Process all +, -, *, / in the top of the operator stack while (!operatorStack.isEmpty() && (operatorStack.peek() == '+' || operatorStack.peek() == '-' || operatorStack.peek() == '*' || operatorStack.peek() == '/')) { processAnOperator(operandStack, operatorStack); } // Push the + or - operator into the operator stack operatorStack.push(token.charAt(0)); } else if (token.charAt(0) == '*' || token.charAt(0) == '/' || token.charAt(0) == '%') { // Process all *, / in the top of the operator stack while (!operatorStack.isEmpty() && (operatorStack.peek() == '*' || operatorStack.peek() == '/' || operatorStack.peek() == '%')) { processAnOperator(operandStack, operatorStack); } // Push the * or / operator into the operator stack operatorStack.push(token.charAt(0)); } else if (token.charAt(0) == '^') { // Process all *, / in the top of the operator stack while (!operatorStack.isEmpty() && operatorStack.peek() == '^') { processAnOperator(operandStack, operatorStack); } // Push the ^ operator into the operator stack operatorStack.push(token.charAt(0)); } else if (token.trim().charAt(0) == '(') { operatorStack.push('('); // Push '(' to stack } else if (token.trim().charAt(0) == ')') { // Process all the operators in the stack until seeing '(' while (operatorStack.peek() != '(') { processAnOperator(operandStack, operatorStack); } operatorStack.pop(); // Pop the '(' symbol from the stack } else { // An operand scanned // Push an operand to the stack operandStack.push(new Integer(token)); } } // Phase 2: process all the remaining operators in the stack while (!operatorStack.isEmpty()) { processAnOperator(operandStack, operatorStack); } // Return the result return operandStack.pop(); } /** Process one operator: Take an operator from operatorStack and * apply it on the operands in the operandStack */ public static void processAnOperator( Stack operandStack, Stack operatorStack) { char op = operatorStack.pop(); int op1 = operandStack.pop(); int op2 = operandStack.pop(); if (op == '+') operandStack.push(op2 + op1); else if (op == '-') operandStack.push(op2 - op1); else if (op == '*') operandStack.push(op2 * op1); else if (op == '/') operandStack.push(op2 / op1); else if (op == '^') operandStack.push((int)Math.pow(op2, op1)); else if (op == '%') operandStack.push(op2 % op1); } public static String insertBlanks(String s) { String result = ""; for (int i = 0; i

Related Questions

Navigate

• Browse (All)
• Browse J
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.