Determine if an expression is valid (C++)

[david220wang385]

Title:

Determine if an expression is valid (C++)

Body:

A valid expression is one that has an equal number of opening and closing braces

[YashikaAggarwal]

I want to contribute to this issue...Is it open ?

[tstreamDOTh]

sure @YashikaAggarwal

[Nandinig24]

Please assign the task to me