Mathematical expressions can be written in 3 different methods - infix, postfix and prefix. Infix notation All these days we have been using infix notation. In this operators are written between the operands. Some operators are having higher priorities than others. If some expressions are enclosed in brackets, then they are evaluated first. e.g. (A+B)*C Here + operator will operate on A and B as it is between them. Though * has higher priority, as A+B is enclosed in brackets, that is evaluated before multiplication. Postfix notation In a postfix notation - also called Reverse Polish Notation, operator is written after the operands. The operator operates on two operands to its immediate left. And expressions are always evaluated from left to right. Brackets do not have any effect on this. e.g. (A+B)*C in postfix is AB+C* A+B*C+D in postfix is ABC*+D+ Prefix notation In a prefix notation, operator is written before the operands. And just like postfix, expressions ...