1. CS005 Introduction to Programming
Matlab
Eamonn Keogh

2. Quick Review of Functions
Let us write a function that gets the user age as an integer
(nothing)
We need a good name for the function…
We need to make sure that even if the use types in a real number, we return an integer. The built-in function round will help.
GetAge
Say the user types in 10.5 10

4. If the person entering their age is under 18, I want to display a warning “You cannot vote” on the screen.
This is called conditional branching

5. Conditional Branching
Get the Users Age
Check if age less than 18
Yes No
Display Warning Message
Return rounded version of Age

6. Conditional Branching
We do conditional Branching with the if statement
function UsersAge = GetAge()
UsersAge = input('Please Enter your age in years : ');
if UsersAge < 18
disp('You cannot vote')
end
UsersAge = round(UsersAge);

7. We do conditional Branching with the if statement
if UsersAge < 18
disp('You cannot vote')
end
if some logical expression is true
do these statements

8. We do conditional Branching with the if statement
if UsersAge < 18
disp('You cannot vote')
end
(Minor note: You can write this on a single line, so long as you put commas after each statement)
if UsersAge < 18, disp('You cannot vote') , end

9. We do conditional Branching with the if statement
if some logical expression is true
do these statements
end
Matlab uses ‘0’ to mean false
Matlab uses ‘1’ to mean true (actually any non-zero)

10. EDU>> 1 + 2 ans = 3 EDU>> 10 < 20 1
When Matlab sees an arithmetic expression such as 1 + 2, it evaluates it:
EDU>> 1 + 2
ans = 3
When you evaluate a arithmetic expression, the answer is always a single number.
When Matlab sees a logical (or relational )expression such as 10 < 20, it evaluates it:
EDU>> < 20 1
When you evaluate a logical expression, the answer is always true or false, which is matlab are represented as 1 and 0

13. We can practice these skills on the Matlab command line.
Here we as saying.. “Matlab, please tell us if two is less than four?”
And Matlab will respond by returning a ‘1’ if it is true (as it happens to be) but a ‘0’ if it is false

14. EDU>> 2 < -7
ans =
EDU>> 2 < abs(-7) 1
EDU>> 2 < max(1,0)
EDU>> 2 < max(1,17)
EDU>> 2 < 2.3
ans = 1
EDU>> 2 < round(2.3)
EDU>> 2 < 1+2
EDU>> 2 < sqrt(9)

15. EDU>> HisAge = 17;
EDU>> 2 < HisAge
ans = 1
EDU>> 2 < min(1,HisAge)
EDU>> 2 < HisAge - 500
EDU>> HisAge < 21
EDU>> HisAge = 17;
EDU>> HerAge = 34;
EDU>> HisAge < HerAge
ans = 1
EDU>> 20 < max(HerAge,HisAge)

16. The relational operators
Math Matlab
 ==
 <
 >
 >=
 <=
 ~=
It is important to differentiate between assignment and comparison for equality
A = B % A is assigned to B
A == B % A equal to B?
~ is the tilde (TILL-duh or TILL-day)
It is usually to the left of ‘1’ key on keyboard

17. EDU>> <= 50
ans = 1
EDU>> <= 2
EDU>> < 2
EDU>> 2 == 4
ans =
EDU>> 2 == 2 1
EDU>> 2 ~= 2
EDU>> 2 ~= 7

18. A Golden Rule ( For all computer languages, not just Matlab)
We should never test for equality or inequality with real numbers
EDU>> == % Do not do this!
ans = 1
EDU>> HisAge = GetAge();
EDU>> HisAge == 18 % Do not do this!
EDU>> round(HisAge) == 18 % But this is OK!
We will see why later….

19. Let us return to this example…
if UsersAge < 18
disp('You cannot vote')
end
(Minor note: You can write this on a single line, so long as you put commas after each statement)
if UsersAge < 18, disp('You cannot vote') , end

20. Let us return to this example…
EDU>> UsersAge = 14;
EDU>> if UsersAge < 18, disp('You cannot vote') , end
You cannot vote
EDU>> UsersAge = 44;
EDU>>

21. More examples… EDU>> UsersAge = 14;
EDU>> if UsersAge < 21, disp('You cannot drink') , end
You cannot drink
EDU>>
EDU>> UsersAge = 55;
EDU>> if UsersAge < 21, disp('You cannot drink') , end
EDU>> if UsersAge >= 55, disp(' senior discount!') , end
senior discount!

22. Boolean Variables (sort of)
Just as we can have variables to hold numbers, for example:
EDU>> HisAge = 12;
EDU>> HerBMI = 23.23;
We can have variables to hold truth values, for example
EDU>> IsMarried = 1; % I have assigned this TRUE
EDU>> IsIrish = 0; % I have assigned this FALSE
It is a great idea to name these variables IsSomething. We may call these variables, Boolean variables (But, at least in Matlab, they are just ordinary numbers)

23. We can have variables to hold truth values, for example
EDU>> IsMarried = 1; % I have assigned this TRUE
EDU>> IsIrish = 0; % I have assigned this FALSE
EDU>> if IsMarried, disp('Hard Luck') , end
Hard Luck
EDU>> if IsIrish, disp('You lucky dog!') , end
EDU>>

24. Only return a 0 or 1, a true or false
Let us write a function that asks a user their age, and returns their voting status. Their voting status is binary (or Boolean), you can either legally vote or not. Here is how we might use it..
EDU>> IsAbleToVote = GetVotingStatus();
EDU>> if IsAbleToVote, disp(‘Please Pull Lever Now:') , end
(nothing)
GetVotingStatus
Only return a 0 or 1, a true or false

25. function VoteStatus = GetVotingStatus()
VoteStatus = 0; % Let us assume she cannot vote
UsersAge = input('Please Enter your age in years : ');
if UsersAge >= 18
VoteStatus = 1; % Let us change our assumption
end

26. Our function seems to work…
EDU>> GetVotingStatus
Please Enter your age in years : 1
ans =
Please Enter your age in years : 33 1

27. Lab assignment will be online during lab Quiz on Monday?
Review Session: Tomorrow 10 to 12, meet here
If you are late, you will miss it (late means, one second after 10:00am)