1. CS005 Introduction to Programming: Matlab
Before MidTerm
After MidTerm
Eamonn Keogh

2. Conditional Branching
Get the Users Age
Check if age less than 18
Yes No
Display Warning Message
Continue…

3. Conditional Branching
Get the Users Age
Check if age less than 18 No
Yes
Display Confirmation Message
Display Warning Message
Continue…

4. Relational Expressions
EDU>> 2 < -7
ans =
EDU>> 2 <= abs(-7) 1
EDU>> 2 == max(2,0)
EDU>> ans = 2 < 7
EDU>> ans = 2 + 7
EDU>> ans = 2 <
EDU>> ans = max(2,1) < 10
EDU>> ans = 2 == 19
EDU>> ans = 2 * 7
EDU>> ans = 2 ~= HisAge + 1
How can we recognize a relational expression?
If there is one of the following <, <=, >, >=, ==, ~=, then it is an relational expression.
Relational expressions evaluative to 1 or 0, nothing else is possible.
Matlab uses ‘0’ to mean false
Matlab uses ‘1’ to mean true

5. We do conditional Branching with the if statement
UsersAge = 12;
if UsersAge < 18
disp('You cannot vote')
end
if some logical expression is true
do these statements
The code here is called the if block (of code).
The if block can have as many lines of code as we like.

6. 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
You should not do this, this is just to allow me to make terser slides

7. We can generalize the if statement to include the else clause
if some logical expression is true
do these statements
else
do these statements instead
end
The if block
The else block
The if block and the else block can be different sizes

8. We can generalize the if statement to include the else clause
UsersAge = 12;
if UsersAge < 18
disp('You cannot vote')
else
disp('You are allowed to vote')
end

9. FishCount = GetNumberOfFish(); if FishCount < 10 disp(' Hard Luck')
else
disp(' Good Catch')
end
In the above code, exactly one of ‘ Hard Luck’ or ‘ Good Catch’ will happen.
There is no way that both could happen, and there is no way neither could happen.
The if with else statement divides the world into two mutually exclusive worlds

10. function UserAge = GetUsersAgeBilingual()
Let us write a function to test our new skill.
Our function gets a users age, prompting her in here choice of English or Spanish
function UserAge = GetUsersAgeBilingual()
LanguageChoice = input('Press 1 for English, Toca 2 para español : ');
if LanguageChoice == 1
UserAge = input('Please Enter your age: ');
else
UserAge = input('Por favor ingrese su edad : ');
end

11. EDU>> WifesAge = GetUsersAgeBilingual()
Press 1 for English, Toca 2 para español : 1
Please Enter your age: 23
WifesAge = 23
Press 1 for English, Toca 2 para español : 2
Por favor ingrese su edad : 19 19
EDU>>

12. function UserAge = GetUsersAgeBilingual()
LanguageChoice = input('Press 1 for English, Toca 2 para español : ');
if LanguageChoice == 1
UserAge = input('Please Enter your age: ');
disp('Thank you');
else
UserAge = input('Por favor ingrese su edad : ');
disp('Gracias')
end

13. EDU>> MothersAge = GetUsersAgeBilingual()
Press 1 for English, Toca 2 para español : 1
Please Enter your age: 67
Thank you
MothersAge = 67
Press 1 for English, Toca 2 para español : 2
Por favor ingrese su edad : 75
Gracias 75

14. Digression function UserAge=GetUsersAgeBilingual() %Bad
Likewise, we will use spaces in an elegant way….
function UserAge=GetUsersAgeBilingual() %Bad
function UserAge = GetUsersAgeBilingual() %Good

15. Digression function UserAge = GetUsersAgeBilingual()
LanguageChoice = input('Press 1 for English, Toca 2 para español : ');
if LanguageChoice == 1
UserAge = input('Please Enter your age: ');
disp('Thank you');
else
UserAge = input('Por favor ingrese su edad : ');
disp('Gracias')
end
Digression
These two functions are identical. In the one below I just removed the blank lines and left justified everything
From now on, all you code should be pretty-print like the above.
I may not always do this in my slides for space reasons.
function UserAge = GetUsersAgeBilingual()
LanguageChoice = input('Press 1 for English, Toca 2 para español : ');
if LanguageChoice == 1
UserAge = input('Please Enter your age: ');
disp('Thank you');
else
UserAge = input('Por favor ingrese su edad : ');
disp('Gracias')
end

16. A classic use of a if/else statement is dividing a number line into two distinct possibilities.
Let us look at age…
Age
Child/Adult 10
Mile per Hour
Speeding?
100
Blood Sugar Count
Diabetic? 40
Net Worth
Rich/Poor
10,000

17. function AdmissionPrice = GetDisneyAdmissionPrice()
AgeOfTicketBuyer = GetUsersAgeBilingual();
if AgeOfTicketBuyer <= 10
AdmissionPrice = 59; % They are a child
else
AdmissionPrice = 80; % They are a adult
end
Age
Child/Adult 10

18. function AdmissionPrice = GetDisneyAdmissionPrice()
AgeOfTicketBuyer = GetUsersAgeBilingual();
if AgeOfTicketBuyer <= 10
AdmissionPrice = 59; % They are a child
else
AdmissionPrice = 80; % They are a adult
end
Age
Child/Adult 10

19. EDU>> ToBill = GetDisneyAdmissionPrice
Press 1 for English, Toca 2 para español : 1
Please Enter your age: 5
Thank you
ToBill = 59

20. Digression function AdmissionPrice = GetDisneyAdmissionPrice()
This code is a little shorter, but logically identical. Either is fine, perhaps the longer one might be easer to read and understand
function AdmissionPrice = GetDisneyAdmissionPrice()
if GetUsersAgeBilingual() <= 10
AdmissionPrice = 59; % They are a child
else
AdmissionPrice = 80; % They are a adult
end
Age
Child/Adult 10

21. We can use the if/else statement to divde the world into two cases:
Adult/Child, English/Spanish, Jew/Gentile
Suppose we have three cases?
Toddler/Child/Adult, English/Spanish/French, Jew/Catholic/Atheist
Matlab allows this with the elseif statement
Toddler
Child
Adult 10
Age

22. 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

23. function AdmissionPrice = NewGetDisneyAdmissionPrice()
AgeOfTicketBuyer = GetUsersAgeBilingual();
if AgeOfTicketBuyer <= 3
AdmissionPrice = 45; % They are a Toddler
elseif AgeOfTicketBuyer <= 10
AdmissionPrice = 59; % They are a Child
else
AdmissionPrice = 80; % They are a Adult
end
This code “goes” left to right
Toddler
Child
Adult 10
Age

24. function AdmissionPrice = NewGetDisneyAdmissionPrice()
AgeOfTicketBuyer = GetUsersAgeBilingual();
if AgeOfTicketBuyer >= 11
AdmissionPrice = 80; % They are a Adult
elseif AgeOfTicketBuyer >= 4
AdmissionPrice = 59; % They are a Child
else
AdmissionPrice = 45; % They are a Toddler
end
This code “goes” right to left
Toddler
Child
Adult 10
Age

25. function UserAge = GetUsersAgeMultilingual()
LanguageChoice = input('1 for English, 2 para español, 3 pour le français : ');
if LanguageChoice == 1
UserAge = input('Please Enter your age: ');
elseif LanguageChoice == 2
UserAge = input('Por favor ingrese su edad : ');
else
UserAge = input('Entrez votre âge? : ');
end
EDU>> GetUsersAgeMultilingual()
1 for English, 2 para español, 3 pour le français : 1
Please Enter your age: 34
ans = 34
1 for English, 2 para español, 3 pour le français : 2
Por favor ingrese su edad : 56 56
1 for English, 2 para español, 3 pour le français : 3
Entrez votre âge? : 78 78

26. HomeWork III (due Wed 1st at 8:10am)
You can do this homework with paper and pen, however you should use four different color pens to highlight the code, as in the sample below.
Print VERY carefully, and remember all syntax, every ; ‘ ‘ ( ) etc
function CigsPerDay = GetUse*****
% Eamonn Keogh
% This program asks the user for***
CigsPerDay = input(' Enter how m..
if CigsPerDay *********************
disp(‘You..***********************
elseif CigsP*************************
disp(‘******************************
else
disp('******************************
end
Write a function that asks the user how many cigarettes a day they smoke, and returns that number.
The function should also display one of three messages for a nonsmoker, a light smoker, and a heavy smoker (you can define the last two)

27. HomeWork III (due Wed 1st at 8:10am)
You can do this homework with paper and pen, however you should use four different color pens to highlight the code.
Write a function in which you pass in one augment, a code for a language.
If the function is called with a ‘1’, display “Felicitaciones”
If the function is called with a ‘2’, display “Parabéns!”
If the function is called with a ‘3’, display “Congratulazioni”
The function will always return NaN.
EDU>> DispCongrats(2)
Parabéns!”
ans =
NaN
function DummayVar = DispCo*****
% Eamonn Keogh
% This program **********
DummayVar =NaN:
if *****************
disp(‘Felicita*********************
elseif *******************