GCD and LCM

#include <iostream>

using namespace std;

int GreatestCommonDivisor(int x,int y);
int LeastCommonMultiple(int x,int y);
void Menu();

int main ()
{
    int a,b,c;
    do
    {
        Menu();
        cin>>c;
        system("CLS");
        switch (c)
        {
            case 1:
                cout<<"Insert New Numbers"<<endl;
                cin>>a>>b;
                break;
            case 2:
                cout<<"Lcm="<<LeastCommonMultiple(a,b)<<endl;
                break;
            case 3:
                cout<<"Gcd="<<GreatestCommonDivisor(a,b)<<endl;
                break;
            case 4:
                cout<<"The Program Is Closing"<<endl;
        system("PAUSE");
                break;
            default:
                cout<<"Wrong Character"<<endl;
        break;
        }
    }while (c!=4);
    return 0;
}

int GreatestCommonDivisor(int x,int y)
{
    int m;
    while (y!=0)
    {
        m=x%y;
        x=y;
        y=m;
    }
    return x;
}

int LeastCommonMultiple(int x,int y)
{
    int lcm;
    lcm=x*y;
    lcm=lcm/GreatestCommonDivisor(x,y);
    return lcm;
}

void Menu()
{
    cout<<"Menu:"<<endl
        <<"1. New numbers."<<endl
        <<"2. Calculation of lcm."<<endl
        <<"3. Calculation of gcd."<<endl
        <<"4. Exit."<<endl;
    return;
}