1. 16.216 ECE Application Programming
Instructor: Dr. Michael Geiger
Fall 2011
Lecture 11: More if examples
Conditional statements—switch

2. ECE Application Programming: Lecture 11
Lecture outline
Announcements/reminders
Today’s office hours: 2:00-3:00 only (ECE dept. meeting)
Assignment 4 posted; due Friday, 10/7
Exam 1: Wednesday, 10/5
Will be allowed one double-sided sheet of notes
Old exams on course website
Assignment 3 grading to be completed soon
Yes, I know … here we go again with this “completed soon” stuff
Once graded, should be able to submit regrades via Blackboard
Will need to me when you resubmit
Another possible Mac (or Windows/Linux) IDE: NetBeans
Today
Range checking with if
More if examples
Conditional statements: switch
2/16/2018
ECE Application Programming: Lecture 11

3. ECE Application Programming: Lecture 11
Review: 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))
May test multiple conditions using if/else if/.../else
Second condition is tested only if first is false; third condition tested only if first two are false, etc.
Else case used only if all previous tests false
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ECE Application Programming: Lecture 11

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!"); }
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ECE Application Programming: Lecture 11

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!");
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ECE Application Programming: Lecture 11

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!");
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ECE Application Programming: Lecture 11

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!");
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ECE Application Programming: Lecture 11

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!");
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ECE Application Programming: Lecture 11

9. Example 1: 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
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ECE Application Programming: Lecture 11

10. ECE Application Programming: Lecture 11
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);
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ECE Application Programming: Lecture 11

11. Example 1 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; }
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ECE Application Programming: Lecture 11

12. Example 1 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; }
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ECE Application Programming: Lecture 11

13. ECE Application Programming: Lecture 3
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
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ECE Application Programming: Lecture 3

14. switch/case statement - General form
switch ( <expression> ) { case <value1> : <statements> [ break; ]
case <value2> : <statements> [ break; ]
: [ default: <statements> [ break; ] ] }
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ECE Application Programming: Lecture 3

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)
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ECE Application Programming: Lecture 11

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
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ECE Application Programming: Lecture 11

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; }
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ECE Application Programming: Lecture 11

18. ECE Application Programming: Lecture 11
Next time
PE2: Conditional statements
Exam 1 Review Monday
Be prepared to ask questions!
2/16/2018
ECE Application Programming: Lecture 11