Notes

import java.util.*;

public class InfixEvulator {

// Method to determine operator precedence
private static int precedence(char op) {
if (op == '+' || op == '-') return 1;
if (op == '*' || op == '/') return 2;
return 0; // For parentheses or invalid characters
}

// Method to apply an operator to two numbers
private static int applyOperation(int a, int b, char op) {
switch (op) {
case '+': return a + b;
case '-': return a - b;
case '*': return a * b;
case '/': return a / b; // Handle division by 0 separately if required
}
return 0;
}

// Method to evaluate an infix expression step-by-step
public static int evaluateInfix(String expression) {
Stack<Integer> values = new Stack<>(); // Operands stack
Stack<Character> operators = new Stack<>(); // Operators stack

System.out.println("Expression: " + expression);

for (int i = 0; i < expression.length(); i++) {
char c = expression.charAt(i);

// Skip spaces
if (c == ' ') continue;

// If a number is found
if (Character.isDigit(c)) {
int num = 0;

// Handle multi-digit numbers
while (i < expression.length() && Character.isDigit(expression.charAt(i))) {
num = num * 10 + (expression.charAt(i) - '0');
i++;
}
i--; // Undo the extra increment
values.push(num); // Push the number to the operand stack
System.out.println("Added to values stack: " + num);
}

// If an open parenthesis is found
else if (c == '(') {
operators.push(c);
System.out.println("Added to operators stack: (");
}

// If a closing parenthesis is found
else if (c == ')') {
System.out.println("Closing parenthesis found, resolving...");
// Process until an open parenthesis is found
while (operators.peek() != '(') {
int b = values.pop();
int a = values.pop();
char op = operators.pop();
int result = applyOperation(a, b, op);
values.push(result);
System.out.println("Operation: " + a + " " + op + " " + b + " = " + result);
}
operators.pop(); // Remove the open parenthesis
System.out.println("Open parenthesis removed from operators stack.");
}

// If an operator is found
else if (c == '+' || c == '-' || c == '*' || c == '/') {
System.out.println("Operator found: " + c);
// Check precedence and process accordingly
while (!operators.isEmpty() && precedence(operators.peek()) >= precedence(c)) {
int b = values.pop();
int a = values.pop();
char op = operators.pop();
int result = applyOperation(a, b, op);
values.push(result);
System.out.println("Operation: " + a + " " + op + " " + b + " = " + result);
}
// Push the current operator to the stack
operators.push(c);
System.out.println("Added to operators stack: " + c);
}
}

// Process remaining operators
System.out.println("Resolving remaining operations...");
while (!operators.isEmpty()) {
int b = values.pop();
int a = values.pop();
char op = operators.pop();
int result = applyOperation(a, b, op);
values.push(result);
System.out.println("Operation: " + a + " " + op + " " + b + " = " + result);
}

// Final result
int finalResult = values.pop();
System.out.println("Final Result: " + finalResult);
return finalResult;
}

public static void main(String[] args) {
String expression = "3 + 5 * ( 2 - 8 )";
evaluateInfix(expression);
}
}