1. EECE.2160 ECE Application Programming
Instructor:
Dr. Michael Geiger
Fall 2018
Lecture 10:
While/do-while examples

2. Announcements/reminders
Text exercises due 3 days after each lecture
Program 1 resubmissions due Tuesday, 2/19
Program 3 due Monday, 2/25
Exam 1 on Friday, 2/22
Allowed one double-sided 8.5” x 11” note sheet
No other notes, no electronic devices
Old exams at link on course home page (
5/25/2019
ECE Application Programming: Lecture 9

3. ECE Application Programming: Lecture 11
Lecture outline
Review
While, do-while loops
Today’s lecture
While loop applications
Do-while loops
Example problems
5/25/2019
ECE Application Programming: Lecture 11

4. ECE Application Programming: Lecture 11
Review: while loops
Used for repetition of code
while (<expression>)
<statement>  loop body
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ECE Application Programming: Lecture 11

5. Application: loop with flexible limit
Could determine loop limit based on variable
Result of calculation
Input value
See while2.c for an example (on website)
Program to calculate average grade
First reads # of grades to enter, then list of grades
Keeps running sum of all grades entered
Calculates average at end
Loop:
while (gradeCount < numGrades) {
scanf("%lf", &grade); // Read grade
gradeSum = gradeSum + grade; // Add to sum
gradeCount = gradeCount + 1; // Inc. count }
5/25/2019
ECE Application Programming: Lecture 11

6. Application: sentinel value
Common to read input until a certain value(sentinel) is entered
May be predetermined (i.e., run program until user enters ‘q’ for “quit”)
Run until invalid value entered
In file input, will often run until end of file
See while3.c for an example (on website)
Refined version of average grade program
Core of program:
// Prompt for and read first grade
printf("Enter grade: ");
scanf("%lf", &grade);
/* Continue reading/accumulating grades until invalid
value entered */
while ((grade >= 0.0) && (grade <= 100.0)) {
gradeSum = gradeSum + grade; // Accumulate grade
gradeCount = gradeCount + 1; // Increment grade count
printf("Enter grade: "); // Prompt for and
scanf("%lf", &grade); // read next grade }
5/25/2019
ECE Application Programming: Lecture 11

7. Review: do-while loops
while loop is pre-tested
Check condition at start; if false, don’t enter loop
To guarantee at least one iteration, use post-tested loop: do-while
Checks condition at end of loop
do { <statements> } while ( <expression> );
Don’t forget semicolon!
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ECE Application Programming: Lecture 11

8. comparison while vs do-while
x = 7; do { printf("%d ",x); x = x + 1; } while ( x < 10 );
OUTPUT:
7 8 9
x = 7; while ( x < 10 ) { printf("%d",x); x = x + 1; }
OUTPUT:
7 8 9
5/25/2019
ECE Application Programming: Lecture 11

9. comparison while vs do-while
x = 7; do { printf("%d",x); x = x + 1; } while ( x < 3 );
OUTPUT: 7
x = 7; while ( x < 3 ) { printf("%d",x); x = x + 1; }
OUTPUT:
(no output)
5/25/2019
ECE Application Programming: Lecture 11

10. Application: sentinel value
Core of program demonstrating while loop
// Prompt for and read first grade
printf("Enter grade: ");
scanf("%lf", &grade);
/* Continue reading/accumulating grades until invalid
value entered */
while ((grade >= 0.0) && (grade <= 100.0)) {
gradeSum = gradeSum + grade; // Accumulate grade
gradeCount = gradeCount + 1; // Increment grade count
printf("Enter grade: "); // Prompt for and
scanf("%lf", &grade); // read next grade }
5/25/2019
ECE Application Programming: Lecture 11

11. Application: sentinel value
Rewrite grade average program to ensure at least one grade is read
Change core of program (shown previously):
/* Prompt for and read grades until invalid
value entered */
do {
printf("Enter grade: "); // Prompt for and
scanf("%lf", &grade); // read grade
if ((grade >= 0.0) && (grade <= 100.0)) {
gradeSum = gradeSum + grade; // Accumulate grade
gradeCount = gradeCount + 1; // Inc. grade count }
} while ((grade >= 0.0) && (grade <= 100.0));
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ECE Application Programming: Lecture 11

12. ECE Application Programming: Lecture 11
Examples
Write a while or do-while loop for each of the following tasks:
Print all multiples of 3 between 0 and 100 (including 0)
Given two variables, x and y, repeatedly increment x by 1 and decrement y by 1 until x is greater than y.
Count the number of iterations this loop takes and print it when the loop is done
Print the initial values of x and y before the loop starts
Repeatedly prompt for and read a single non-space character into a variable, cmd, until the user enters either 'X' or 'x'.
5/25/2019
ECE Application Programming: Lecture 11

13. ECE Application Programming: Lecture 11
Example solutions
Print all multiples of 3 between 0 and 100 (including 0)
int i = 0;
while (i < 100) {
printf("%d\n", i);
i = i + 3; }
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ECE Application Programming: Lecture 11

14. Example solutions (continued)
Given two integer variables, x and y, repeatedly increment x by 1 and decrement y by 1 until x is greater than y.
Print the initial values of x and y before the loop starts
Count the number of iterations this loop takes and print it when the loop is done
int x, y;
int i = 0; // i = # iterations
... // Code to assign values to x & y
printf("x = %d, y = %d initially\n", x, y);
while (x <= y) {
x = x + 1;
y = y - 1;
i = i + 1; }
printf("Number of iterations: %d\n", i);
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ECE Application Programming: Lecture 11

15. Example solutions (continued)
Repeatedly prompt for and read a single non-space character into a variable, cmd, until the user enters either 'X' or 'x'.
char cmd;
do {
printf("Enter character: ");
scanf(" %c", &cmd);
} while (cmd != 'X' && cmd != 'x');
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ECE Application Programming: Lecture 11

16. ECE Application Programming: Lecture 11
Final notes
Next time
Exam 1 Preview
Reminders:
Text exercises due 3 days after each lecture
Program 1 resubmissions due Tuesday, 2/19
Program 3 due Monday, 2/25
Exam 1 on Friday, 2/22
Allowed one double-sided 8.5” x 11” note sheet
No other notes, no electronic devices
Old exams at link on course home page (
5/25/2019
ECE Application Programming: Lecture 11