(Evaluate expression) Modify Listing 20.12, EvaluateExpression.java, to add operators ^ for exponent and % for remainder. 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 Here is the Listing 20.12 to modify: import java.util.Stack; public class EvaluateExpression { 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(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) == '/') { // 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 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); } 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; } }
(Evaluate expression) Modify Listing 20.12, EvaluateExpression.java, to add
operators ^ for exponent and % for remainder. 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
Here is the Listing 20.12 to modify:
import java.util.Stack; public class EvaluateExpression { 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(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<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; } }
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