I have three warnings on this program:

#include <iostream.h>

int get_month ();
int get_day ();
int get_year ();
int display (int,int,int);

void main ()
{
int dia, mes, anos;
dia=get_day ();
mes=get_month ();
anos=get_year ();
display(dia,mes,anos);
return;
}

int get_day ()
{
int i;
cout << "\nPlease enter day of brith ";
cin >> i;
return i;
}
int get_month ()
{
int hate;
cout << "\nPlease enter month of brith ";
cin >> hate;
return hate;
}

int get_year ()
{
int functions;
cout << "\nPlease enter year of birth ";
cin >> functions;
return functions;
}

int display (int dia, int mes, int anos)
{
cout << "";
return 0;
}


I cant find the problem, please help.