RPN(Reverse Polish Notation) calculator

Javascript RPN Scientific Calculator

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Reverse Polish Notation (RPN) is a method of expressing arithmetic expressions in which the operator is placed after its operands. This differs from the more common infix notation, in which the operator is placed between the operands. RPN is also known as postfix notation, and it is used in many computer languages and calculators.

An RPN calculator is a calculator that uses RPN notation to perform arithmetic operations. In this article, we will discuss the basics of RPN notation and how to build an RPN calculator.

RPN notation is based on the concept of a stack. A stack is a data structure that follows the Last-In-First-Out (LIFO) principle. This means that the last element added to the stack is the first one to be removed. In an RPN calculator, the operands are pushed onto the stack, and the operators are applied to the top elements of the stack.

Let's take an example of how an RPN calculator works. Suppose we want to evaluate the expression 3 + 4 * 5. In RPN notation, this expression would be written as 3 4 5 * +. We start by pushing 3 onto the stack. Then we push 4 and 5 onto the stack. The next operation is multiplication, which we apply to the top two elements of the stack (4 and 5). The result of the multiplication (20) is pushed onto the stack. Finally, we apply the addition operator to the top two elements of the stack (3 and 20) and get the final result of 23.

Now let's see how we can implement an RPN calculator in Python. We start by defining a stack class:

python
class Stack:
    def __init__(self):
        self.items = []

    def push(self, item):
        self.items.append(item)

    def pop(self):
        return self.items.pop()

    def peek(self):
        return self.items[-1]

    def is_empty(self):
        return len(self.items) == 0

The Stack class has four methods:

• push(item): adds an item to the top of the stack.
• pop(): removes and returns the top item from the stack.
• peek(): returns the top item from the stack without removing it.
• is_empty(): returns True if the stack is empty, False otherwise.

Next, we define a function to evaluate an RPN expression:

python
def evaluate(expression):
    stack = Stack()
    for token in expression.split():
        if token.isdigit():
            stack.push(int(token))
        else:
            operand2 = stack.pop()
            operand1 = stack.pop()
            if token == "+":
                result = operand1 + operand2
            elif token == "-":
                result = operand1 - operand2
            elif token == "*":
                result = operand1 * operand2
            elif token == "/":
                result = operand1 / operand2
            stack.push(result)
    return stack.pop()

The evaluate function takes an RPN expression as input and returns its value. It starts by creating a stack object. It then iterates over the tokens in the expression. If a token is a number, it is converted to an integer and pushed onto the stack. If a token is an operator (+, -, *, /), the top two items are popped from the stack, the operation is applied, and the result is pushed onto the stack. Finally, the function returns the result of the expression.

Let's test our RPN calculator with some examples:

python
>>> evaluate("3 4 5 * +")
23
>>> evaluate("5 2 /")
2.5
>>> evaluate("4 5 * 6 -")
14

In conclusion, an