concatenar 3 numeros

[bichorendon]

coneste codigo concateno dos caracteres necesito concatenar 3 caracteres

lcd_putc("\fDay: ");
day=get2_bcd(); ///llama la operacion concatenar numeros entrantes
///en el keyboard

byte get2_bcd() {
char first,second;

do {
first=kbd_getc();
} while ((first<'0') || (first>'9'));
lcd_putc(first);
first-='0';

do {
second=kbd_getc();
} while ((second<'0') || (second>'9'));
lcd_putc(second);

ptr=strcat (fist,second);

return((first<<4)|(second-'0')); //retorna dos numeros concatenados
}