There are two ways (in my knowledge) one can evaluate an infix expression. One: By the use of lexical analysing and parsing. Or, using some low-grade method to mimic that parsing, convert that into postfix, and evaluating the postfix. I did the latter. This applies the knowledge of data structures and algorithms, for I've implemented stack, queue and algorithms like "Shunting Yard Algorithm

Complete code can be seen below: https://github.com/nootanghimire/calc-cpp