Join 2 integers

Good evening

Meanwhile I remembered something... and it works!

char Debug[40];
char* cstr(int Parametro){
itoa(Parametro,Debug,10);
return strdup(Debug);
}

char *concatena(char *string1, char *string2) {
strcpy(StringFinal, string1);
strcat (StringFinal, string2);
return StringFinal;
}

DD=atoi(concatena(cstr(Dia1),cstr(Dia2)));

Thanks
Best regards
Pedro Ferrer