Recursive grep question

> Goal:
> -Find the string "foobar" every place that it occurs in the *.c files
> in all of the subX directories.
>
> Command and result:
> [adayley@locatlhost top]$ grep -ir foobar *.c
> grep: *.c: No such file or directory
> [adayley@locatlhost top]$
>
> Question:
> I gave the 'r' option for a recursive search and I know that the subX
> diretories have *.c files. But, grep appearently does not decend into
> the subX directories because the top directory has no *.c files. How
> do I make it search the subX directories anyway?
>
> Alan

ps. it is not decending into any directories because no directories have
a name that matches *.c. (The star is matched before grep even runs.)