Use a stack to store numbers.

When a number is found, push it onto the stack. When an operator is found, pop the last two numbers, apply the operator in the correct order, and push the result back. At the end, the stack contains the final answer.

Reverse Polish Notation does not need parentheses because the operator position defines evaluation order.

Pseudocode:

function evaluateRpnExpression(tokens, size):
    stack = empty stack
    for each token in tokens:
        if token is a number:
            push number into stack
        else:
            right = pop stack
            left = pop stack
            result = apply token to left and right
            push result into stack
    return top of stack