Please solve this question

4. Write below programs. a. Using a do-while statement, write a C program to accept a grade. The program should request a grade continuously as long as a valid grade is entered. An invalid grade is any grade less than 0 or greater than 100. After a valid grade has been entered, your program should display its value. (10 pts) b. Modify the program written for a. so that the user is alerted when an invalid grad has been entered. (10 pts) c. Modify the program written in b. so that it allows the user to exit the program by entering the number 999. (10 pts) -END