Validate a Boolean expression with brackets in C#

Question

I want to validate a string in C# that contains a Boolean expression with brackets. The string should only contain numbers 1-9, round brackets, \"OR\" , \"AND\".

Exa

Answer 1

Pretty simply:

At first stage you must determ lexems (digit, bracket or operator) with simple string comparsion.

At second stage you must define variable of count of closed bracket (bracketPairs), which can be calculated by the following algorithm for each lexem:

if current lexem is '(', then bracketPairs++;

if current lexem is ')', then bracketPairs--.

Else do not modify bracketPairs.

At the end if all lexems are known and bracketPairs == 0 then input expression is valid.

The task is a bit more complex, if it's necesery to build AST.