man uisdigit () - Tells if a character is a digit. Allegro game programming library.
NAME
uisdigit - Tells if a character is a digit. Allegro game programming library.
SYNOPSIS
#include <allegro.h>
int uisdigit(int c);
DESCRIPTION
Returns nonzero if `c' is a digit.
for (counter = 0; counter < ustrlen(text_string); counter++) {
if (uisdigit(ugetat(text_string, counter)))
usetat(text_string, counter, '*');
}