grep.... I know I am new to ubuntu but....

I have a directory structure, inside that are a number of .c source files. I want to find which of those files contain certain strings. 
In a DOS window using grep I would type
grep "mystring" -i *.c
this would result in a list of .c files containing the string.

If I try similar strings with ubuntu even with ack-grep which is supposed to be an improvement I keep getting told that *.c no such file or directory. 

Even trying the various bizarre combinations of finds and execs that I have seen on the web I can't seem to do this very simple task. If Microsoft can have managed to provide find in files and various other similar things for over 20 years isn't it time I could do the same on a linux system without the need to spend 10 hours searching endless uninformative websites all lying about what works?