This program is a postfix evaluator. It reads information from a file given on the command line and computes the answer (sum, difference, quotient, or product) and prints out the answer.
In postfix, the operator comes after its two operands. Below are a few expressions with infix on the left and the postfix equivalent on the right (extra spacing added for readability): 6-9→69- 4+52→452+ 45-2→452-
Postfix expressions are simpler to evaluate than are infix expressions because there are no parentheses or precedence rules. Instead, expressions are evaluated in the order the operands and operators appear. It is for this reason that compilers and interpreters generally translate infix expressions into postfix, and then generate assembly code that carries out the postfix computation.