using getline(), it jumps to the next thing. c++

    int userin;
    string name;
    string firstname;
    string lastname;
    string dob;

	bool exit_b= false;   
while(exit_b == false){

    cout<<"\nmake a new customer enter: 1"<<endl;
    cout<<"\nmake a new staff enter: 2"<<endl;
    cin>>userin;

    if(userin ==1)
        {
            cout<<"Enter First Name: "<<endl;
            cin>>firstname;

            cout<<"Enter Last Name: "<<endl;
            cin>>lastname;
            name = firstname + " " + lastname;


            cout<<"Date Birth: "<<endl; //this thing should take user input
            getline(cin,dob);   //but this thing doesnt take input it jumps to the next part of the code

            Customer customer(name, dob, rand()%10000);
            customer.print_detail();
        }