We can use getchar() as well in place of cin.ignore(). Here is my code :

int i1;
double d1;
string s1;

cin >> i1;
cin >> d1;
getchar();//cin.ignore();
getline(cin,s1);

s.append(s1);
cout << i+i1 <<endl<<fixed<<setprecision(1)<<d+d1 <<endl <<s;