Expression Math In String to Double

is there a time in your programming life when you meet such as changing
your math expression string x="3,14*(5^2)+(10^2)" like that or etc.
than what you need is an engine expression parser

May be below link can help and make life easier.
:)

http://www.c-sharpcorner.com/uploadfile/patricklundin/mathexpparser12062005062213am/mathexpparser.aspx