• The selector must be an integral expression (int, char, long); it can't be a float or double
• The case label must be a literal or named constant (const); an expression can be used, but the operands must be literals and/or constants
• Each case usually ends with a break statement; if no break statement is present, the statements in the next case that follows will be executed
• Notice that you don't need curly braces around the multiple statements that are part of each case:

switch (grade)
{
   case 'P' :
      cout << "You are passing." << endl;
      cout << "Therefore, you will get credit";
      cout << endl;
      break;

   case 'N' :
      cout << "You are NOT passing." << endl;
      cout << "Therefore, you will NOT get credit";
      cout << endl;
      break;

   default  :
      cout << "Grade must be P or N" << endl;
      break;
}