1. 16.216 ECE Application Programming
Instructor: Dr. Michael Geiger
Spring 2012
Lecture 14: Range checking, switch statements

2. ECE Application Programming: Lecture 14
Lecture outline
Announcements/reminders
Program 4 due today; Program 5 to be posted ASAP
Regrades on previous programs coming (no, really)
Exams to be returned Wednesday
Midterm feedback forms on Wednesday
Today
Review: if
Range checking with if
switch statements
7/4/2018
ECE Application Programming: Lecture 14

3. Review: conditional statements
Conditional execution using if statements:
Form:
if (<expression>)
<statement>
[ else brackets show
<statement> ] else is optional
Expression frequently uses relational operators to test equality/inequality
< > <= >= == !=
e.g., if (x <= 5)
Can combine conditions using logical operators
AND : && OR: ||
e.g., if ((x <= 5) && (x > 0))
Can test if condition is false using logical NOT: !
e.g., if (!(x < 5))
7/4/2018
ECE Application Programming: Lecture 14

4. if (range checking - take 1)
int n;
printf("Enter a number 1 to 10: "); scanf("%d",&n); if (n > 10) { printf(“That’s not in range!"); } else if (n < 1) { printf(“That’s not in range!"); } else { printf("Good job!"); }
7/4/2018
ECE Application Programming: Lecture 14

5. if (range checking - take 2)
If there is only one statement needed for the true and/or false condition, the {} are not needed
int n;
printf("Enter a number 1 to 10: "); scanf("%d",&n); if (n > 10) printf(“That’s not in range!"); else if (n < 1) printf(“That’s not in range!"); else printf("Good job!");
7/4/2018
ECE Application Programming: Lecture 14

6. if (range checking - take 3)
Use the && or || as needed to check for multiple conditions
int n;
printf("Enter a number 1 to 10: "); scanf("%d",&n); Note these ( ) are needed
if ( (n > 10) || (n < 1) ) printf(“That’s not in range!"); else printf("Good job!");
7/4/2018
ECE Application Programming: Lecture 14

7. if (range checking - take 4)
Use the && or || as needed to check for multiple conditions
int n;
printf("Enter a number 1 to 10: "); scanf("%d",&n); Note these ( ) are needed
if ( (1 <= n) && (n <= 10) ) printf(“Good job!"); else printf(“That’s not in range!");
7/4/2018
ECE Application Programming: Lecture 14

8. if (range checking) (The WRONG WAY)
int n;
printf("Enter a number 1 to 10: "); scanf("%d",&n);
if (1 <= n <= 10 ) // THIS WILL NOT COMPILE printf("Good job!"); else printf(“That’s not in range!");
7/4/2018
ECE Application Programming: Lecture 14

9. Example: if statements
Write a short code sequence to do each of the following:
Given int x, check its value
If x is greater than 5 and less than or equal to 10, print x
Prompt for and read temperature as input (type double)
If temp is 90 or higher, print “It’s too hot!”
If temp is 32 or lower, print “It’s freezing!”
In all other cases, print “It’s okay”
Read 3 int values and print error if input problem
Values are separated by a comma
If fewer than 3 values read, print error message with number of values
Example: Error: only 2 inputs read correctly
7/4/2018
ECE Application Programming: Lecture 14

10. ECE Application Programming: Lecture 14
Example 1 solution
Given int x, check its value
If x is greater than 5 and less than or equal to 10, print x
if ((x > 5) && (x <= 10))
printf(“%d\n”, x);
7/4/2018
ECE Application Programming: Lecture 14

11. Example solution (cont.)
Prompt for and read temperature as input (type double)
If temp is 90 or higher, print “It’s too hot!”
If temp is 32 or lower, print “It’s freezing!”
In all other cases, print “It’s okay”
int main() {
double temp;
printf(“Enter temperature: “);
scanf(“%lf”, &temp);
if (temp >= 90)
printf(“It’s too hot!\n”);
else if (temp <= 32)
printf(“It’s too cold!\n”);
else
printf(“It’s okay\n”);
return 0; }
7/4/2018
ECE Application Programming: Lecture 14

12. Example solution (cont.)
Read 3 int values and print error if input problem
Values are separated by a comma
If fewer than 3 values read, print error message with number of values
Example: Error: only 2 inputs read correctly
int main() {
int x, y, z; // Input values
int num; // # values read
num = scanf(“%d,%d,%d”, &x, &y, &z);
if (num < 3)
printf(“Error: only %d inputs read correctly”,
num);
return 0; }
7/4/2018
ECE Application Programming: Lecture 14

13. ECE Application Programming: Lecture 14
switch statements
Nesting several if/else if statements can get tedious
If each condition is simply checking equality of same variable or expression, can use switch
7/4/2018
ECE Application Programming: Lecture 14

14. switch/case statement - General form
switch ( <expression> ) { case <value1> : <statements> [ break; ]
case <value2> : <statements> [ break; ] .
. [ default: <statements> [ break; ] ] }
7/4/2018
ECE Application Programming: Lecture 14

15. switch/case statement
Check if <expression> matches any value in case statements
If <expression> == <value1>, execute <statements> in that case
If <expression> == <value2>, execute <statements> in that case
If <expression> does not equal any of the values, go to default case (if present)
7/4/2018
ECE Application Programming: Lecture 14

16. Switch statements and break
Each case is just a starting point—switch does not automatically skip other cases!
Example:
switch (x) {
case 0:
x = 3;
case 1:
x = x * 4;
default:
x = x – 1; }
If x == 0:
Start at case 0  x = 3;
Then, go to case 1  x = x * 4 = 3 * 4 = 12
Then, go to default:  x = x – 1 = 12 – 1 = 11
7/4/2018
ECE Application Programming: Lecture 14

17. 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; }
7/4/2018
ECE Application Programming: Lecture 14

18. switch/case statement - example
#include <stdio.h>
int main() { char grd; printf("Enter Letter Grade: "); scanf("%c",&grd); printf(“You are ");
// continued next slide
7/4/2018
ECE Application Programming: Lecture 14

19. 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; }
7/4/2018
ECE Application Programming: Lecture 14

20. 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:
7/4/2018
ECE Application Programming: Lecture 14

21. ECE Application Programming: Lecture 14
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
7/4/2018
ECE Application Programming: Lecture 14

22. 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; }
7/4/2018
ECE Application Programming: Lecture 14

23. ECE Application Programming: Lecture 14
Next time
Exam 1 Review
Midterm feedback
7/4/2018
ECE Application Programming: Lecture 14