$1.$ Write a C$++$ program that does the following:

a$.$ Create a C$++$ file with the name problem$4.$cpp$.$

b$.$ Prompt the user to enter a sequence of numeric grades until the user enters a negative grade.

c$.$ Compute and print the average grade.

Sample run of the program:

Enter a numeric grade $($enter a negative number to stop$)$: $78$

Enter a numeric grade $($enter a negative number to stop$)$: $89$

Enter a numeric grade $($enter a negative number to stop$)$: $77$

Enter a numeric grade $($enter a negative number to stop$)$: $90$

Enter a numeric grade $($enter a negative number to stop$)$: $97$

Enter a numeric grade $($enter a negative number to stop$)$: $92$

Enter a numeric grade $($enter a negative number to stop$)$: $-1$

The average grade is $87\mathrm{.}1667$