This box represents the block of code to execute
if the first case is a match. (case 'A':)


That is, if the value of the variable Grade is 'A',
then the code under case 'A': will be executed.

printf ("Excellent \n");
break;

The printf statement will cause the word "Excellent"
to be output, and then the break; will cause 
execution of the switch to be finished.