Dev - C++ - Ayuda con un programa que dada una fecha que me diga el día de la semana

#include <iostream>

using namespace std;

int DiaDeLaSemana( int dia, int mes, int anyo )

{

    int A = (14 - mes) / 12;

	int Y = anyo - A;

	int M =  mes + (12 * A) - 2;

    int diaSemana;

    if (anyo >=  1582)       /// Inicio del calendario Gregoriano

        diaSemana = ( dia + Y + Y/4 - Y/100 + Y/400 + (31 * M)/12 ) % 7;

    else        /// calendario Juliano

        diaSemana = ( 5 + dia + Y + Y/4 + (31 * M)/12 ) % 7;

	if (diaSemana > 0) diaSemana--;

	else  diaSemana = 6;

	return diaSemana;

}

int main()

{

    int dia, mes, anyo;

    cout << "Dia: "; cin >> dia;

    cout << "Mes: "; cin >> mes;

    cout << "Anyo: "; cin >> anyo;

    switch(DiaDeLaSemana(dia, mes, anyo)) {

        case 0: cout << "\nLunes." << endl; break;

        case 1: cout << "\nMartes." << endl; break;

        case 2: cout << "\nMiercoles." << endl; break;

        case 3: cout << "\nJueves." << endl; break;

        case 4: cout << "\nViernes." << endl; break;

        case 5: cout << "\nSabado." << endl; break;

        case 6: cout << "\nDomingo." << endl; break;

    }

    return 0;

}