I got rid of the cin>>dummy; and put a cin.ignore outside the for loop
#include <string>
#include <iostream>
using namespace std ;
int main()
{
string name ;
cout << "Please enter your full name: ";
cin >> name ;
cout << "Welcome " << name << endl ;
cout << "Please re-enter your full name: " ;
// Uncomment the next line to correct this program.
cin.ignore( 256, '\n' );
getline( cin, name ) ;
cout << "Thanks, " << name << endl ;
return 0 ;
}