if (mark < 50)
   grade = 'F';     // i.e. FL
else if (mark < 65)
   grade = 'P';     // i.e. PS
else if (mark < 75)
   grade = 'C';     // i.e. CR
else if (mark < 85)
   grade = 'D';     // i.e. DN
else
   grade = 'H';     // i.e. HD