Homework SourseE1516 Add a remainder operator to the expression calculator
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);
}
}
Solution
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);
}
}
