1. CS005 Introduction to Programming:
Matlab
Eamonn Keogh

2. Conditional Branching
The if statement
Get the Users Score
Selectively run some code
Check if score less than 90
Yes No
Display Warning Message
Continue…

3. Conditional Branching
The if/else statement
Get the Users Score
Selectively run one of two code options
Check if score less than 90 No
Yes
Display Confirmation Message
Display Warning Message
Continue…

4. Conditional Branching
The if/elseif statement
Get the Users Score
Selectively run one of three or more code options
Check score
Display A
Display B
Display C
Display Fail
Continue…

5. We can further generalize the if/else statement to include the elseif clause
if some logical expression is true
do these statements
elseif some other logical expression is true
do these statements instead
else
end
The if block
The elseif block
The else block
In the above code, exactly one block will happen.
There is no way that two or three could happen, and there is no way none could happen.
This elseif statement divides the world into three mutually exclusive worlds

6. The last generalization of the if/elseif statement is it realize that we can have more than one elseif
if some logical expression is true
do these statements
elseif some other logical expression is true
do these statements instead
elseif yet another logical expression is true
else
end
The if block
First elseif block
Second elseif block
The else block
In the above code, exactly one block will happen.
There is no way that more than one could happen, and there is no way none could happen.
This elseif statement divides the world into three or more mutually exclusive worlds

7. GetExamScore Let us write a function that: Failing C B A
Asks a user to enter the grade they got out of 100
Echoes the letter grade to the screen
Returns that grade
(No input parameters)
GetExamScore
(echo letter grade) 79
Failing C B A 70 80 90
100
score

8. function Score = GetExamScore() Score = input('Enter your score : ');
if Score >= 90
disp('A quality work');
elseif Score >= 80
disp('B quality work');
elseif Score >= 70
disp('C quality work');
else
disp('Failing');
end
EDU>> EamonnsScore = GetExamScore()
Enter your score : 99
A quality work
EamonnsScore = 99

9. Wrong! function Score = GetExamScore()
Score = input('Enter your score : ');
if Score >= 90
disp('A quality work');
elseif Score >= 80
disp('B quality work');
elseif Score >= 70
disp('C quality work');
elseif Score >= 0
disp('Failing');
end
Wrong!
Common mistake
The last block of code must be a else, not an elseif. (contrast with previous slide)

10. GetHeight Let us write a function that: Short Tall
Asks a user to enter their height in feet (no inches)
Echoes the {tall,medium,short} to the screen
Returns their height in feet (no inches)
(No input parameters)
If you are taller than 6 foot, you are tall
If you are 5 foot, you are medium
If you are 4 foot or shorter, you are short
GetHeight
(echo height) 4
Medium
Short
Tall 5 6
Height

11. In this code it is never possible to be short, only tall or medium.
function Height = GetHeight()
% Has bug
Height = input('Enter your height in feet only : ');
if Height >= 6
disp('Tall');
elseif Height < 6
disp('Medium');
else
disp('Short');
end
In this code it is never possible to be short, only tall or medium.
function Height = GetHeight()
Height = input('Enter your height in feet only : ');
if Height >= 6
disp('Tall');
elseif Height >= 5
disp('Medium');
else
disp('Short');
end
We need to test all the breakpoints (critical values), plus or minus 1

12. Tall Short Short Tall Short Short Medium Medium Medium 6 5
Tall 6 5
Medium
Short
Medium
Short
Tall
if Height >= 6 5 6
Medium
Short
elseif Height >= 5 5 6
Short
else 5

13. We can have if statements inside of if statements
We can have if statements inside of if statements. This is called nesting.
if some logical expression is true
else
do these statements instead
end
if some logical expression is true
do these statements
else
do these statements instead
end
The if block
The else block

14. GetUserCode Let us write a function that:
Asks a user to enter their sex and age
Returns a code, from one to four
1 : man
2 : woman
3: boy
4: girl
Echoes the persons label to the screen
(No input parameters)
EDU>> GetUserCode
Enter 1 for male, 2 for female : 1
Enter your age : 55
Man
Enter 1 for male, 2 for female : 2
Enter your age : 5
Girl
GetUserCode
(echo person label) 4

15. function Label = GetUserCode()
sex = input('Enter 1 for male, 2 for female : ');
age = input('Enter your age : ');
if sex == 1
disp('Male');
else
disp('Female');
end
Let us build up to it.
Let us ignore age for now, and ignore the return value.
This code just correctly displays male/female
EDU>> GetUserCode
Enter 1 for male, 2 for female : 2
Enter your age : 2
Female
EDU>>

16. Let us ignore the return value for now
function Label = GetUserCode()
sex = input('Enter 1 for male, 2 for female : ');
age = input('Enter your age : ');
if sex == 1
if age >= 18
disp('Man');
else
disp('Boy');
end
disp('Woman');
disp('Girl');
Let us build up to it.
Let us ignore the return value for now
This code just correctly displays man/woman/boy/girl
EDU>> GetUserCode
Enter 1 for male, 2 for female : 1
Enter your age : 1
Boy
Enter your age : 55
Man
Enter 1 for male, 2 for female : 2
Enter your age : 2
Girl
Woman
EDU>>

17. The whole thing. function Label = GetUserCode()
sex = input('Enter 1 for male, 2 for female : ');
age = input('Enter your age : ');
if sex == 1
if age >= 18
disp('Man');
Label = 1;
else
disp('Boy');
Label = 3;
end
disp('Woman');
Label = 2;
disp('Girl');
Label = 4;
The whole thing.

18. function Label = GetUserCode()
sex = input('Enter 1 for male, 2 for female : ');
age = input('Enter your age : ');
if sex == 1
if age >= 18
disp('Man');
Label = 1;
else
disp('Boy');
Label = 3;
end
disp('Woman');
Label = 2;
disp('Girl');
Label = 4;
As an aside, we can begin to appreciate how important pretty printing is