I tried some methods but found it difficult because of the decimal point. can somebody suggest an easy method?

Can you be more specific as to what methods you have tried already ? Else you'll get a dozen answers, each with a method that you have already tried !

But why is the decimal point a problem ? Floating point math routines should handle this detail without any need for the programmer to step in.

The most common way to calculate a square root would be a Newton iteration. As Per said, this is pretty much trivial to implement and converges quickly.