getline function

hi, i am facing a strange problem in use of getline. i have used    ---   cin.getline(p.name,'\n' ) --- but it only picks first 10 characters and as a result corrupts next inputs. if i use - cin.getline(p.name,80 ) then it works well. please help me that why the first statement is not working correctly. for the reference i m pasting the code below  

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# include <iostream.h>
# include <conio.h>
     struct Person{
     char name[50];
     long phoneNumber;
     char gender;
     int age;
     };
void main()
{
     Person p;
     cout << "Enter name of person: " ;
     cin.getline(p.name,'\n' );                            // problem line
     cout << "Enter phone number: ";
     cin >> p.phoneNumber;
     cout << "Enter gender: ";
     cin >> p.gender;
     cout << "Enter age: ";
     cin >> p.age;
     cout<<"Name: "<<p.name<<"\n";
     cout<<"Phone Number: "<<p.phoneNumber<<"\n";
     cout<<"Gender: "<<p.gender<<"\n";
     cout<<"Age: "<<p.age<<"\n";
     getch ();
}
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regards
fa.