If the grade entered is greater than or equal to zero...
(Display Listing 7.)
If the grade entered by the user is greater than or equal to zero:
The code in the body of the loop is executed.
The first statement in the body of the loop adds the new grade to the sum, which was initialized to a value of zero when it was declared.
Assuming the grade values that are entered are greater than zero, the value of sum increases during each iteration of the body of the loop.