How do I validate letter grade is valid?

[jafa]

Hello,
Part of my assignment is to validate that the entered grade is either A, B, C, D or F.
What am I doing wrong?
Here is the what I am trying but it doesn't work:


for (int i = 1; i <= 6; i++)
{

cout << "Enter letter grade for class " << i << endl;
cin >> grade;
while (grade != 'A' || grade != 'B' || grade != 'C' || grade != 'D' || grade != 'F')
{
cout << "Please enter a valid letter grade for class " << i << endl;
cin >> grade;
}
}

[JLBorges]

// while (grade != 'A' || grade != 'B' || grade != 'C' || grade != 'D' || grade != 'F')
while( grade != 'A' && grade != 'B' && grade != 'C' && grade != 'D' && grade != 'F' )

[jafa]

Thanks JLBorges so much!!!