Given an postfix expression, solve the expression and calculate the expression

Use a stack and process tokens from left to right. Numeric tokens are pushed. For an operator, require two available operands, pop right first and left second, then evaluate left operator right and push the result. The pop order is essential for subtraction, division, and exponentiation. At the end, exactly one stack value should remain; otherwise the input contains too many operands or too few operators. Explain how numbers are tokenized if values can be multi-digit or negative: splitting whitespace is safer than iterating characters. State division behavior, including truncation versus floating point and division-by-zero errors, rather than allowing language defaults to be implicit. Test a single operand, negative values, nested operations, invalid operator placement, and extra operands. Every token is processed a constant number of times, so runtime is O(n) and worst-case stack space is O(n).