In mathematics, an expression or mathematical expression is a finite combination of symbols that is well-formed according to rules, like PEMDAS. In computers, expression can be hard to calculate with precedence rules and user input errors to handle computer math we often convert strings into a notation like rpn to solve the problem.
A Tech Talk on user inputs using Javascript. The grade calculator takes multiple values and does a calculation on them. User input can be useful for other projects, such as being used as a query.