Why is cin.ignore() necessary when using “getline” after “cin”, but is not required when using “cin” multiple times?

Question

In my knowledge when using getline() after cin, we need to flush the newline character in the buffer first, before calling getline(),

Answer 1

signed main(){
    /*
     * input is of next two lines
     * Stack Overflow
     * Where developers learn.
     * for more about cin.ignore visit http://www.cplusplus.com/reference/istream/istream/ignore/
     */
    string name, address;
    cin>>name;
    //cin.ignore();
    //cin.ignore(256,'\n');
    getline(cin,address);
    cout << address << endl;
    assert(address == " Overflow"); // breaks if using cin.ignore() or cin.ignore(256,'\n')
    assert(address == "Overflow"); // breaks if using cin.ignore(256,'\n') OR not using any
    assert(address == "Where developers learn."); // breaks if using cin.ignore() or not using ignore
}

enter the input

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