vậy hoy đi nha

#include<iostream.h>
#include<conio.h>
void nhap(int *n);
void menu(int n);
void snt(int n);
void khung(void);
void chiahetxandy(int x,int y,int n);//truyen tham so x,y chia het cho x va y
void chiahetxandkhongchiahety(int x,int y,int n);//truyen tham so x,y chia het cho x va khong chia het y
void snt1toin(int n);
int demso(int n);
void chusnt(int n);
void tongchusnt(int n);
void tichchusnt(int n);
void chusochan(int n);
void tongchusochan(int n);
void tichchusochan(int n);
int main()
{
    int n;
    nhap(&n);
    menu(n);
}
void menu(int n)
{
    int a;
    do
    {
        cout<<endl<<"ban da nhap n="<<n;
        cout<<endl<<"1: nhap lai n";
        cout<<endl<<"2: kiem tra so nguyen to";
        cout<<endl<<"3: kiem tra cac so tu 1 toi "<<n<<" chia het cho 2 va 3";
        cout<<endl<<"4: kiem tra cac so tu 1 toi "<<n<<" chia het cho 5 va khong chia het cho 8";
        cout<<endl<<"5: kiem tra cac so nguyen to tu 1 toi "<<n;
        cout<<endl<<"6: kiem tra cac chu so la so nguyen to ";
        cout<<endl<<"7: kiem tra tong cac chu so la so nguyen to ";
        cout<<endl<<"8: kiem tra tich cac chu so la so nguyen to ";
        cout<<endl<<"9: kiem tra cac chu so la so chan ";
        cout<<endl<<"10: kiem tra tong cac chu so chan ";
        cout<<endl<<"11: kiem tra tich cac chu so chan ";
        cout<<endl<<"0: thoat";
        cout<<endl<<"ban muon con chuc nang nao: ";cin>>a;
        while(!(cin))
        {
            cin.clear();
            cin.ignore();
            system("cls");
            cout<<"ban da nhap sai hay nhap lai";
            cout<<endl<<"ban da nhap n="<<n;
            cout<<endl<<"1: nhap lai n";
            cout<<endl<<"2: kiem tra so nguyen to";
            cout<<endl<<"3: kiem tra cac so tu 1 toi "<<n<<" chia het cho 2 va 3";
            cout<<endl<<"4: kiem tra cac so tu 1 toi "<<n<<" chia het cho 5 va khong chia het cho 8";
            cout<<endl<<"5: kiem tra cac so nguyen to tu 1 toi "<<n;
            cout<<endl<<"6: kiem tra cac chu so la so nguyen to ";
            cout<<endl<<"7: kiem tra tong cac chu so la so nguyen to ";
            cout<<endl<<"8: kiem tra tich cac chu so la so nguyen to ";
            cout<<endl<<"9: kiem tra cac chu so la so chan ";
            cout<<endl<<"10: kiem tra tong cac chu so chan ";
            cout<<endl<<"11: kiem tra tich cac chu so chan ";
            cout<<endl<<"0: thoat";
            cout<<endl<<"ban muon con chuc nang nao: ";cin>>a;
        }
        switch(a)
        {
            case 1:system("cls");nhap(&n);break;
            case 2:system("cls");khung();snt(n);khung();break;
            case 3:system("cls");chiahetxandy(2,3,n);break;
            case 4:system("cls");chiahetxandkhongchiahety(5,8,n);break;
            case 5:system("cls");snt1toin(n);break;
            case 6:system("cls");chusnt(n);break;
            case 7:system("cls");tongchusnt(n);break;
            case 8:system("cls");tichchusnt(n);break;
            case 9:system("cls");chusochan(n);break;
            case 10:system("cls");tongchusochan(n);break;
            case 11:system("cls");tichchusochan(n);break;
            case 0:exit(0);break;
        }
        if(a<0||a>11)
        {
            system("cls");
            cout<<"ban da nhap sai hay nhap lai";
        }
    }while(true);

}
void snt(int n)
{
    int tam=0;
    for(int i=2;i<=n-1;i++)
    {
        if(n%i==0)
        {
            tam=1;
            break;
        }
    }
    if(tam==0)
    cout<<n<<" la so nguyen to"<<endl;
    else
    cout<<n<<" khong la so nguyen to"<<endl;
}
void khung(void)
{
    cout<<"-------------------------------------------------------------------------------"<<endl;
}
void nhap(int *n)
{
    do
    {
        cout<<"nhap so nguyen n:";
        cin>>*n;
        while(!(cin))
        {
            cin.clear();
            cin.ignore(256,'\n');
            system("cls");
            cout<<"nhap sai hay nhap lai"<<endl;
            cout<<"nhap so nguyen n:";
            cin>>*n;
        }
        if(*n<=0)
        {
            system("cls");
            cout<<"nhap sai hay nhap lai"<<endl;
        }
    }while(*n<=0);
    system("cls");
}
void chiahetxandy(int x,int y,int n)
{
    int tam=0;
    khung();
    cout<<"cac so tu 1 toi "<<n<<" chia het cho "<<x<<" va "<<y<<" la: ";
    for(int i=1;i<=n;i++)
    {
        if(i%x==0&&i%y==0)
        {
            cout<<i<<" ";
            tam=1;
        }
    }
    cout<<endl;
    khung();
    if(tam==0)
    {
        system("cls");
        khung();
        cout<<"khong co so chia het cho "<<x<<" va "<<y<<endl;
        khung();
    }
}
void chiahetxandkhongchiahety(int x,int y,int n)
{
    int tam=0;
    khung();
    cout<<"cac so tu 1 toi "<<n<<" chia het cho "<<x<<" va khong chia het "<<y<<" la: ";
    for(int i=1;i<=n;i++)
    {
        if(i%x==0&&i%y!=0)
        {
            cout<<i<<" ";
            tam=1;
        }
    }
    cout<<endl;
    khung();
    if(tam==0)
    {
        system("cls");
        khung();
        cout<<"khong co so chia het cho "<<x<<" va khong chia het "<<y<<endl;
        khung();
    }
}
void snt1toin(int n)
{
    int tam,tam1=0;
    khung();
    cout<<"cac so nguyen to tu 1 toi "<<n<<" la: ";
    for(int i=1;i<=n;i++)
    {
        tam=0;
        for(int j=2;j<=i-1;j++)
        {
            if(i%j==0)
            tam=1;
        }
        if(tam==0)
        cout<<i<<" ";
    }
    cout<<endl;
    khung();
}
int demso(int n)
{
    int i=n,t=0;
    while(i/10!=0)
    {
        i/=10;
        t++;
    }
    return t+1;
}
void chusnt(int n)
{
    int a,tam,tam1=0;
    a=demso(n);
    khung();
    cout<<"cac chu so la so nguyen to la: ";
    for(int i=1;i<=a;i++)
    {
        tam=0;
        for(int j=2;j<=(n%10)-1;j++)
        {
            if((n%10)%j==0)
            {
                tam=1;
            }

        }
        if(tam==0)
        {
            tam1=1;
            cout<<n%10<<" ";
        }
        n/=10;
    }
    cout<<endl;
    khung();
    if(tam1==0)
    {
        system("cls");
        khung();
        cout<<"khong co chu so nao la so nguyen to"<<endl;
        khung();
    }
}
void tongchusnt(int n)
{
    int a,tam,tam1=0,s=0;
    a=demso(n);
    khung();
    for(int i=1;i<=a;i++)
    {
        tam=0;
        for(int j=2;j<=(n%10)-1;j++)
        {
            if((n%10)%j==0)
            {
                tam=1;
            }

        }
        if(tam==0)
        {
            tam1=1;
            s+=n%10;
        }
        n/=10;
    }
    if(tam1==0)
    {
        system("cls");
        khung();
        cout<<"khong co chu so nao la so nguyen to"<<endl;
        khung();
    }
    else
    {
        system("cls");
        khung();
        cout<<"tong cac chu so la so nguyen to la: "<<s<<endl;
        khung();
    }
}
void tichchusnt(int n)
{
    int a,tam,tam1=0,s=1;
    a=demso(n);
    khung();
    for(int i=1;i<=a;i++)
    {
        tam=0;
        for(int j=2;j<=(n%10)-1;j++)
        {
            if((n%10)%j==0)
            {
                tam=1;
            }

        }
        if(tam==0)
        {
            tam1=1;
            s*=n%10;
        }
        n/=10;
    }
    if(tam1==0)
    {
        system("cls");
        khung();
        cout<<"khong co chu so nao la so nguyen to"<<endl;
        khung();
    }
    else
    {
        system("cls");
        khung();
        cout<<"tich cac chu so la so nguyen to la: "<<s<<endl;
        khung();
    }
}
void chusochan(int n)
{
    int a,s=0;
    a=demso(n);
    for(int i=1;i<=a;i++)
    {
        if((n%10)%2==0)
        s++;
        n/=10;
    }
    if(s==0)
    {
        khung();
        cout<<"khong co chu so chan"<<endl;;
        khung();
    }
    else
    {
        khung();
        cout<<"co "<<s<<" chu so chan"<<endl;;
        khung();
    }
}
void tongchusochan(int n)
{
    int a,s=0;
    a=demso(n);
    for(int i=1;i<=a;i++)
    {
        if((n%10)%2==0)
        s+=n%10;
        n/=10;
    }
    if(s==0)
    {
        khung();
        cout<<"khong co chu so chan"<<endl;;
        khung();
    }
    else
    {
        khung();
        cout<<"tong cac chu so chan la: "<<s<<endl;;
        khung();
    }
}
void tichchusochan(int n)
{
    int a,s=1;
    a=demso(n);
    for(int i=1;i<=a;i++)
    {
        if((n%10)%2==0)
        s*=n%10;
        n/=10;
    }
    if(s==1)
    {
        khung();
        cout<<"khong co chu so chan"<<endl;;
        khung();
    }
    else
    {
        khung();
        cout<<"tich cac chu so chan la: "<<s<<endl;;
        khung();
    }
}