The while Looping StructureReview: Repetition StructureThe while Repetition StructureExampleGood Programming PracticeAnother while Loop ExampleThe PseudocodeThe C CodeVersatile?New PseudocodeNew C CodeWhy Bother to Make It Easier?Using a Sentinel ValueThe Priming ReadSlide 15Slide 16Final “Clean” C CodeSlide 18Using a while Loop to Check User InputThe while Looping StructureTopicsThe while LoopProgram VersatilitySentinel Values and Priming ReadsChecking User Input Using a while LoopReadingSection 3.7Review: Repetition StructureA repetition structure allows the programmer to specify that an action is to be repeated while some condition remains true.There are three repetition structures in C, the while loop, the for loop, and the do-while loop.The while Repetition Structurewhile ( condition ){ statement(s)}The braces are not required if the loop body contains only a single statement. However, they are a good idea and are required by the 104 C Coding Standards.Examplewhile ( children > 0 ){ children = children - 1 ; cookies = cookies * 2 ;}Good Programming PracticeAlways place braces around the body of a while loop.Advantages:Easier to readWill not forget to add the braces if you go back and add a second statement to the loop bodyLess likely to make a semantic errorIndent the body of a while loop 3 to 5 spaces -- be consistent!Another while Loop ExampleProblem: Write a program that calculates the average exam grade for a class of 10 students.What are the program inputs?the exam gradesWhat are the program outputs?the average exam gradeThe Pseudocode<total> = 0<grade_counter> = 1While (<grade_counter> <= 10) Display “Enter a grade: ”Read <grade> <total> = <total> + <grade> <grade_counter> = <grade_counter> + 1End_while<average> = <total> / 10Display “Class average is: “, <average>#include <stdio.h>int main ( ){ int counter, grade, total, average ; total = 0 ; counter = 1 ; while ( counter <= 10 ) { printf (“Enter a grade : “) ; scanf (“%d”, &grade) ; total = total + grade ; counter = counter + 1 ; } average = total / 10 ; printf (“Class average is: %d\n”, average) ; return 0 ;}The C CodeVersatile?How versatile is this program?It only works with class sizes of 10.We would like it to work with any class size.A better way :Ask the user how many students are in the class. Use that number in the condition of the while loop and when computing the average.New Pseudocode<total> = 0<grade_counter> = 1Display “Enter the number of students: “Read <num_students>While (<grade_counter> <= <num_students> ) Display “Enter a grade: ” Read <grade> <total> = <total> + <grade><grade_counter> = <grade_counter> + 1End_while<average> = <total> / <num_students>Display “Class average is: “, <average>New C Code#include <stdio.h>int main ( ){ int numStudents, counter, grade, total, average ; total = 0 ; counter = 1 ;  printf (“Enter the number of students: “) ; scanf (“%d”, &numStudents) ; while ( counter <= numStudents) { printf (“Enter a grade : “) ; scanf (“%d”, &grade) ; total = total + grade ; counter = counter + 1 ; } average = total / numStudents ; printf (“Class average is: %d\n”, average) ; return 0 ;}Why Bother to Make It Easier?Why do we write programs? So the user can perform some taskThe more versatile the program, the more difficult it is to write. BUT it is more useable.The more complex the task, the more difficult it is to write. But that is often what a user needs.Always consider the user first.Using a Sentinel ValueWe could let the user keep entering grades and when he’s done enter some special value that signals us that he’s done.This special signal value is called a sentinel value.We have to make sure that the value we choose as the sentinel isn’t a legal value. For example, we can’t use 0 as the sentinel in our example as it is a legal value for an exam score.The Priming ReadWhen we use a sentinel value to control a while loop, we have to get the first value from the user before we encounter the loop so that it will be tested and the loop can be entered.This is known as a priming read.We have to give significant thought to the initialization of variables, the sentinel value, and getting into the loop.New Pseudocode<total> = 0<grade_counter> = 1Display “Enter a grade: “Read <grade>While ( <grade> != -1 ) <total> = <total> + <grade><grade_counter> = <grade_counter> + 1 Display “Enter another grade: ” Read <grade>End_while<average> = <total> / <grade_counter>Display “Class average is: “, <average>New C Code#include <stdio.h>int main ( ){ int counter, grade, total, average ; total = 0 ; counter = 1 ; printf(“Enter a grade: “) ; scanf(“%d”, &grade) ; while (grade != -1) { total = total + grade ; counter = counter + 1 ; printf(“Enter another grade: “) ; scanf(“%d”, &grade) ; } average = total / counter ; printf (“Class average is: %d\n”, average) ; return 0 ;}Final “Clean” C Code#include <stdio.h>int main ( ){ int counter ; /* counts number of grades entered */ int grade ; /* individual grade */ int total; /* total of all grades */ int average ; /* average grade */ /* Initializations */ total = 0 ; counter = 1 ;/* Get grades from user */ /* Compute grade total and number of grades */ printf(“Enter a grade: “) ; scanf(“%d”, &grade) ; while (grade != -1) { total = total + grade ; counter = counter + 1 ; printf(“Enter another grade: “) ; scanf(“%d”, &grade) ; } /* Compute and display the average grade */ average = total / counter ; printf (“Class average is: %d\n”, average) ; return 0 ;}Using a while Loop to Check User Input#include <stdio.h>int main ( ){ int number ; printf (“Enter a positive integer : “) ; scanf (“%d”, &number) ; while ( number <= 0 ) { printf (“\nThat’s incorrect. Try again.\n”) ;  printf (“Enter a positive integer: “) ; scanf (“%d”, &number) ; } printf