Find in files using Vim

Using vim native function

:vim "string a ser buscada"  **/*.c

Or using external tool

:grep "string a ser buscada"  **/*.c


To repeat search for next match use

:cnext

To show a list of occurences and select the file use

:cw  or :copen

To make it easier put it in your .vimrc
nmap <F2> :cnext<CR>