Hi RajniRamShinde and welcome to bytes.com!
Do you know what a prototype is? If not first of all you should check out
the wikipedia article on function prototypes. Basically it is a function definition which shows the signature; in C/C++ these are often in header files though they don't have to be.
Once you've understood that, you can create your own prototype for
capture before it is ever used or defined. What this will look like depends on your function
capture. If you have problems writing it, post the signature of your function (normally the first line of the function) and we'll help you write the prototype.