RPN Expression Evaluator

Personal Project
This Java program parses and evaluates infix expressions by internally converting them to Reverse Polish Notation (RPN) using custom-built stack-based logic. It handles a wide range of operators and parentheses — including +, -, *, /, ^, sin, cos, log, and complex nested expressions.

💡 Features

• ✅ Custom **generic Stack** implementation from scratch (no `java.util.Stack`)
• ✅ Expression validation with error handling for:
  • Unmatched parentheses
  • Consecutive operators
  • Empty expressions
  • Division by zero (handled with NaN, Infinity, -Infinity)
• ✅ Supports unary operators like sin, cos, log
• ✅ File-based batch evaluation via input.txt
• ✅ Throws clear, customized error messages for malformed inputs

🔗 GitHub Repository

View Full Code on GitHub

🔧 Code Snippet: Stack Implementation

```java public class Stack { private int top = -1; private int capacity; private ArrayList arrayList = new ArrayList<>();

public Stack(int capacity) {
    this.capacity = capacity;
}

public boolean push(T val) {
    top++;
    arrayList.add(top, val);
    return true;
}

public T pop() throws IndexOutOfBoundsException {
    if (top < 0) throw new IndexOutOfBoundsException("Empty Stack");
    return arrayList.remove(top--);
}

public T peek() {
    if (top < 0) throw new IndexOutOfBoundsException("Empty Stack");
    return arrayList.get(top);
}

public boolean isEmpty() {
    return top < 0;
}

public int size() {
    return arrayList.size();
} }