1. EECE.2160 ECE Application Programming
Instructors:
Dr. Michael Geiger & Dr. Lin Li
Spring 2019
Lecture 10:
Switch statements; while loops

2. Announcements/reminders
Text exercises due 3 days after each lecture
Lecture Tuesday, not Monday next week
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 (
4/24/2019
ECE Application Programming: Lecture 9

3. ECE Application Programming: Lecture 9
Today’s lecture
Review
Range checking
Switch statements
Switch example
While/do-while loops
4/24/2019
ECE Application Programming: Lecture 9

4. Review: switch statements
When checking multiple exact values for expression, more sense to use switch statement
switch (<expr>) {
case <val1> :
...
break;
case <val2> :
default: }
break allows you to exit switch statement after completing code
Otherwise, program will continue to run through cases until finding break
default covers any values without specific case
4/24/2019
ECE Application Programming: Exam 1 Preview

5. ECE Application Programming: Lecture 9
Switch example
int x; … switch (x) { case 0: y = y + 1; break; case 1: case 2: y = y – 1; default: y = 0; }
4/24/2019
ECE Application Programming: Lecture 9

6. Switch statements and break
Use break to exit at end of case
You may not always want to use break—will see examples later
Rewriting previous example:
switch (x) {
case 0:
x = 3;
break;
case 1:
x = x * 4;
default:
x = x – 1; }
4/24/2019
ECE Application Programming: Lecture 9

7. switch/case statement - example
#include <stdio.h>
int main() { char grd; printf("Enter Letter Grade: "); scanf("%c",&grd); printf(“You are ");
// continued next slide
4/24/2019
ECE Application Programming: Lecture 9

8. switch/case statement - example
switch (grd) { case 'A' :
printf("excellent"); break; case 'B' :
printf("good"); break; case 'C' :
printf("average"); break; case 'D' :
printf("poor"); break; case 'F' :
printf("failing"); break; default :
printf(“incapable of reading directions"); break; } return 0; }
4/24/2019
ECE Application Programming: Lecture 9

9. Example: switch statement
What does the program on the previous slides print if the user enters: A B+ c X
Recognize, of course, that it always prints:
Enter Letter Grade:
4/24/2019
ECE Application Programming: Lecture 9

10. ECE Application Programming: Lecture 9
Example solution
What does the program on the previous slides print if the user enters: A
You are excellent B+
Only first character is read—’B’
You are good c
This program is case-sensitive—’C’ and ‘c’ are two different characters!
Will go to default case
You are incapable of reading directions X
No case for ‘X’—goes to default case
4/24/2019
ECE Application Programming: Lecture 9

11. switch/case statement - Alt example
switch (grd) { case 'A' : case 'a': case 'B' : case 'b': printf("doing very well"); break; case 'C' : case 'c': case 'D' : case 'd': printf("not doing too well"); break; case 'F' : case ‘f': printf("failing"); break; default :
printf("incapable of reading directions"); break; } return 0; }
4/24/2019
ECE Application Programming: Lecture 9

12. ECE Application Programming: Lecture 9
Repetition
Say we have a program to print squares of numbers between 0 and 10:
void main() {
int i; // Number to square
int iSquared; // Square of the number
printf(" i i^2\n"); // Column headings
// Compute and display the squares of numbers 0 through 10
i = 0;
iSquared = i * i;
printf("%2d%10d\n", i, iSquared);
... // Code for i = 1, 2, ... 8, 9
i = 10; }
4/24/2019
ECE Application Programming: Lecture 9

13. ECE Application Programming: Lecture 9
while loops
Previous program does same thing 11 times
Repetitive code can be captured in a loop
Much less code to do same amount of work
Simplest form: while loop
while (<expression>)
<statement>  loop body
Loop body will repeat as long as <expression> is true
Loop body must therefore change expression
<statement> may be one or more lines
If multiple lines, need { } to denote block
4/24/2019
ECE Application Programming: Lecture 9

14. ECE Application Programming: Lecture 9
4/24/2019
ECE Application Programming: Lecture 9

15. ECE Application Programming: Lecture 9
while loops - example
x = 7; while ( x < 10 ) { printf("%d ",x); x = x + 1; }
OUTPUT:
7 8 9
4/24/2019
ECE Application Programming: Lecture 9

16. ECE Application Programming: Lecture 9
while loops - example
x = 7; while ( x < 3 ) { printf("%d ",x); x = x + 1; }
OUTPUT:
(no output)
Possible to have while loop body that never executes!
4/24/2019
ECE Application Programming: Lecture 9

17. Repetition with while loop
Rewriting previous program with loop
int main() {
int i; // Number to square
int iSquared; // Square of the number
printf(" i i^2\n"); // Column headings
// Compute and display the squares of numbers 0 to 10
i = 0; // Initialize i
while (i <= 10) { // Loop until i > 10
iSquared = i * i;
printf("%2d%10d\n", i, iSquared);
i = i + 1; // Increment i }
return 0;
4/24/2019
ECE Application Programming: Lecture 9

18. 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 }
4/24/2019
ECE Application Programming: Lecture 11

19. ECE Application Programming: Lecture 11
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!
4/24/2019
ECE Application Programming: Lecture 11

20. 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
4/24/2019
ECE Application Programming: Lecture 11

21. 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)
4/24/2019
ECE Application Programming: Lecture 11

22. ECE Application Programming: Lecture 9
Final notes
Next time
Loop examples
Reminders:
Text exercises due 3 days after each lecture
Lecture Tuesday, not Monday next week
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 (
4/24/2019
ECE Application Programming: Lecture 9