Why does GCC allow '$' character in variable and function names?

[Sajish V]

I think that C does not allow special characters ( '~' '!' '@' '#' '$' '%' '^' '&' '*' ) in variable and function names. My knowledge is purely based on the books that I have been reading to learn C.

To verify this when I tried to compile a C program using GCC with '$' in variable names and function names I found that GCC does not complain. No errors or warnings. 

I used the basic command with no option to compile. 

bash$ gcc <filename>

Can someone please let me know why GCC allows '$' character in variable and function names?

Thanks.