Mixing char and int types as parameters in portable (summary).

[Doug Gwyn]

' ' is NOT a char, despite appearances.  It is an int.  So is 'ab'.

Actual arguments to functions are widened depending on type (this is a
side-effect of the PDP-11 implementation, now embedded in the language).
Chars are widened to ints and floats are widened to doubles.

Therefore it makes little sense to declare the formal parameters of a
function to be type char or float, since actual arguments never will be.