upcase-region

upcase-region is an interactive built-in function in `C source code'.

It is bound to C-x C-u.

(upcase-region BEG END)

Convert the region to upper case. In programs, wants two arguments.
These arguments specify the starting and ending character numbers of
the region to operate on. When used as a command, the text between
point and the mark is operated on.
See also `capitalize-region'.