Regex required: It should match for following patterns

Question

Valid:

1. ((int)10)
2. (int)10
3. ((char)((x+y)&1))
4. ((int *)1)

Invalid:

Answer 1

The language of (balanced) parenthesized expressions is not regular, i.e., you can't write a regular expressions matching these kind of strings.

See SO question: Why are regular expressions called "regular" expressions and Wikipedia: Regular Languages.

You need to work with a more capable parsing technique such as a CFG with for instance ANTLR.

You could start with something like:

CastedExpression ::= Cast Expression | LPAR CastedExpression RPAR
Cast             ::= LPAR Type RPAR
Expression       ::= Sum | Product | Litteral | LPAR Expression RPAR | ...
Type             ::= char | int | Type ASTERISK | ...

(Feel free to edit grammar above if you find any obvious improvements).