E15.16 Add a % (remainder) operator to the expression calculator of Section 15.6
ID: 3939401 • Letter: E
Question
E15.16 Add a % (remainder) operator to the expression calculator of Section 15.6.3.
package collections;
import java.util.Scanner;
import java.util.Stack;
public class ExpressionCalculator {
public static void main(String[] args) {
Scanner consoleIn = new Scanner(System.in);
System.out.println("Enter an expression: ");
String expression = consoleIn.nextLine().replaceAll("\s+", "");
consoleIn.close();
Stack<Integer> numstack = new Stack<Integer>();
Stack<Character> opstack = new Stack<Character>();
int pos = 0;
while (pos < expression.length()) {
char ch = expression.charAt(pos);
pos += 1;
if (isOperator(ch)) {
if (opstack.size() == 0) {
opstack.push(ch);
} else {
char previousOp = opstack.pop();
if (precedence(ch) > precedence(previousOp)) {
opstack.push(previousOp);
} else {
evaluateTop(numstack, previousOp);
}
opstack.push(ch);
}
} else if (ch == '(') {
opstack.push(ch);
} else if (ch == ')') {
boolean done = false;
while (!done) {
if (opstack.size() == 0) {
printError("No matching");
}
char previousOp = opstack.pop();
if (previousOp == '(') {
done = true;
} else {
evaluateTop(numstack, previousOp);
}
}
} else if (Character.isDigit(ch)) {
int start = pos - 1;
while (pos < expression.length() && Character.isDigit(expression.charAt(pos))) {
pos += 1;
}
String number = expression.substring(start, pos);
numstack.push(Integer.parseInt(number));
} else {
printError("Number, operator or parenthesis expected.");
}
}
while (opstack.size() > 0) {
char previousOp = opstack.pop();
if (previousOp == '(') {
printError("No matching");
} else {
evaluateTop(numstack, previousOp);
}
}
if (numstack.size() == 0) {
printError("Invalid expression");
}
System.out.println(numstack.pop());
if (numstack.size() > 0) {
printError("Invalid expression");
}
}
public static boolean isOperator(char ch) {
return ch == '+' || ch == '-' || ch == '*' || ch == '/';
}
public static void printError(String message) {
System.out.println("ERROR! " + message);
System.exit(1);
}
public static int precedence(char ch) {
if (ch == '+' || ch == '-') {
return 1;
} else if (ch == '*' || ch == '/') {
return 2;
} else {
return 0;
}
}
public static void evaluateTop(Stack<Integer> stack, char operator) {
if (stack.size() == 0) {
printError("Invalid expression");
}
int y = stack.pop();
if (stack.size() == 0) {
printError("Invalid expression");
}
int x = stack.pop();
int z = 0;
if (operator == '*') {
z = x * y;
} else if (operator == '/') {
if (y == 0) {
printError("Divide by 0");
} else {
z = x / y;
}
} else if (operator == '+') {
z = x + y;
} else if (operator == '-') {
z = x - y;
} else {
printError("Syntax error");
}
stack.push(z);
}
}
Explanation / Answer
package collections;
import java.util.Scanner;
import java.util.Stack;
public class ExpressionCalculator {
public static void main(String[] args) {
Scanner consoleIn = new Scanner(System.in);
System.out.println("Enter an expression: ");
String expression = consoleIn.nextLine().replaceAll("\s+", "");
consoleIn.close();
Stack<Integer> numstack = new Stack<Integer>();
Stack<Character> opstack = new Stack<Character>();
int pos = 0;
while (pos < expression.length()) {
char ch = expression.charAt(pos);
pos += 1;
if (isOperator(ch)) {
if (opstack.size() == 0) {
opstack.push(ch);
} else {
char previousOp = opstack.pop();
if (precedence(ch) > precedence(previousOp)) {
opstack.push(previousOp);
} else { evaluateTop(numstack, previousOp);
}
opstack.push(ch);
}
} else if (ch == '(') {
opstack.push(ch);
} else if (ch == ')') {
boolean done = false;
while (!done) {
if (opstack.size() == 0) {
printError("No matching");
}
char previousOp = opstack.pop();
if (previousOp == '(') {
done = true;
} else {
evaluateTop(numstack, previousOp);
}
}
} else if (Character.isDigit(ch)) {
int start = pos - 1;
while (pos < expression.length() && Character.isDigit(expression.charAt(pos))) {
pos += 1;
} String number = expression.substring(start, pos);
numstack.push(Integer.parseInt(number));
} else {
printError("Number, operator or parenthesis expected.");
}
}
while (opstack.size() > 0) {
char previousOp = opstack.pop();
if (previousOp == '(') {
printError("No matching");
} else {
evaluateTop(numstack, previousOp);
}
}
if (numstack.size() == 0) {
printError("Invalid expression");
}
System.out.println(numstack.pop());
if (numstack.size() > 0) {
printError("Invalid expression");
}
}
public static boolean isOperator(char ch) {
return ch == '+' || ch == '-' || ch == '*' || ch == '/' || ch == '%';
}
public static void printError(String message) { System.out.println("ERROR! " + message);
System.exit(1);
}
public static int precedence(char ch) {
if (ch == '+' || ch == '-') {
return 1;
} else if (ch == '*' || ch == '/' || ch == '%') {
return 2;
} else {
return 0;
}
}
public static void evaluateTop(Stack<Integer> stack, char operator) {
if (stack.size() == 0) {
printError("Invalid expression");
}
int y = stack.pop();
if (stack.size() == 0) {
printError("Invalid expression");
}
int x = stack.pop();
int z = 0;
if (operator == '*') {
z = x * y;
} else if (operator == '/') {
if (y == 0) {
printError("Divide by 0");
} else {
z = x / y;
}
} else if (operator == '+') {
z = x + y; } else if (operator == '-') {
z = x - y;
}
else if(operator=='%')
{
z=x%y;
}
else {
printError("Syntax error");
}
stack.push(z);
}
}
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