1. Eamonn Keogh eamonn@cs.ucr.edu
CS005 Introduction to Programming: Matlab
Eamonn Keogh

2. Swapping two numbers EDU>> HisAge = 25; EDU>> HerAge = 48;
Let us say we have assigned two variables, HisAge and HerAge…
However we realize that we have made a mistake, we gave the wrong ages to the wrong person…

3. Swapping two numbers EDU>> HisAge = 25; EDU>> HerAge = 48;
EDU>> HerAge = HisAge;
EDU>> HisAge = HerAge;
We can just swap them….

4. Swapping two numbers NO! EDU>> HisAge = 25;
EDU>> HerAge = 48;
EDU>> HerAge = HisAge;
EDU>> HisAge = HerAge;
EDU>> HerAge
HerAge = 25
EDU>> HisAge
HisAge =
We can just swap them….
NO!
Look at the values…

5. Swapping two numbers EDU>> HisAge = 25; EDU>> HerAge = 48;
EDU>> Temp = HisAge;
EDU>> HisAge = HerAge;
EDU>> HerAge = Temp;
EDU>>
EDU>> HisAge
HisAge = 48
EDU>> HerAge
HerAge = 25
We need a temp variable

6. DeBlanking a String 'do geese see god' 'dogeeseseegod'
EDU>> MyPass = 'do geese see god'
MyPass =
do geese see god
EDU>> DeBlank(MyPass)
ans =
dogeeseseegod
EDU>> DeBlank('do geese see god')
Sometimes it is useful to remove blank spaces from strings…
'do geese see god'
DeBlank
'dogeeseseegod'

7. function DeBlankedString = DeBlank(S) for i = 1 : length(S) disp(S(i))
end
EDU>> DeBlank('do geese see god') d o g e s

8. function DeBlankedString = DeBlank(S) DeBlankedString = [];
for i = 1 : length(S)
if S(i) ~= ' '
disp(S(i));
end
EDU>> DeBlank('do geese see god') d o g e s

9. function DeBlankedString = DeBlank(S) DeBlankedString = [];
for i = 1 : length(S)
if S(i) ~= ' '
DeBlankedString = [DeBlankedString S(i)];
end
EDU>> DeBlank('do geese see god')
dogeeseseegod
EDU>> DeBlank('eamonn john keogh')
ans =
eamonnjohnkeogh

10. Reversing an Array [ 4, 2, 9, 7] [ 7, 9, 2, 4]
EDU>> ReverseMe([ 4, 2, 9, 7])
ans =
Let us write a function that takes in an array, and returns it reversed
[ 4, 2, 9, 7]
ReverseMe
[ 7, 9, 2, 4]

11. function Reversed = ReverseMe(InputArray)
for i = 1 : length(InputArray)
disp( InputArray(i) );
end
EDU>> ReverseMe([ 4, 2, 9, 7]) 4 2 9 7

12. function Reversed = ReverseMe(InputArray) Len = length(InputArray);
for i = 1 : Len
disp( InputArray(i) );
end
EDU>> ReverseMe([ 4, 2, 9, 7]) 4 2 9 7

13. function Reversed = ReverseMe(InputArray) Len = length(InputArray);
for i = 1 : Len
disp( InputArray( Len i ) );
end
EDU>> ReverseMe([ 4, 2, 9, 7]) 7 9 2 4

14. function Reversed = ReverseMe(InputArray) Len = length(InputArray);
for i = 1 : Len
Reversed(i) = InputArray( Len i );
end
EDU>> ReverseMe([ 4, 2, 9, 7])
ans =

15. EDU>> ReverseMe([ 4, 2, 9, 7])
ans =
EDU>> ReverseMe([ 4 ]) 4
EDU>> ReverseMe([ inf])
Inf

16. Testing for Palindromes
Let us write a function that takes in string, and returns true if it is an palindrome, otherwise it returns false
EDU>> Palindrome('radar')
ans = 1
EDU>> Palindrome(‘eamonn')
'radar'
Palindrome 1

17. Testing for Palindromesk e o g h

18. function IsPalindrome = Palindrome(S)
SLen = length(S);
for i = 1 : SLen
disp( S(i) )
end
EDU>> Palindrome(‘radar') r a d
EDU>> Palindrome('eamonn') e a m o n

19. function IsPalindrome = Palindrome(S) SLen = length(S);
for i = 1 : SLen
disp( S(SLen i) )
end
EDU>> Palindrome(‘radar') r a d
EDU>> Palindrome('eamonn') n o m a e

20. function IsPalindrome = Palindrome(S) SLen = length(S);
for i = 1 : SLen
disp( S(i) )
disp( S(SLen i) )
disp('****************')
end
EDU>> Palindrome(‘radar') r
**************** a d
EDU>> Palindrome('eamonn') e n
**************** a
...(deleted for clarity)

21. function IsPalindrome = Palindrome(S) SLen = length(S);
for i = 1 : SLen
if S(i) ~= S(SLen i)
IsPalindrome = 0;
end
EDU>> Palindrome('radar')
ans = 1
EDU>> Palindrome('eamonn')

22. Our palindrome function works on single word palindromes: radar, level, rotor, kayak, redder, madam
It works on some multiword palindromes: step on no pets
It does not work on most multiword palindromes: a man, a plan, a canal Panama,  Madam, Im Adam, never odd or even , rise to vote sir 
We could fix that, with DeBlank()

23. Last times slides are below for ref

24. Searching Arrays
Many problems involve searching an array (including a string) for special values.
Examples include
Searching an array for the largest value (which player in my team makes the most money?)
Searching an array for a particular value (do I have a student with the ID ?)
Searching a string for a particular value(s) ( Does this string “control” have vowels? CNTRL)

25. Searching Arrays
Many problems involve searching an array (including a string) for special values.
These problems are so important that Matlab has special build-in functions to solve some of them.
We have seen:
EDU>> max([ ])
ans = 8
However, let us write some of these function from scratch to build our skill set…

26. Finding Existence of a Given Number
EDU>> TeamAges = [ 5 , 6, 11, 9 , 8];
EDU>> AgeToFind = 9;
EDU>> EamonnsFindNumber(TeamAges,AgeToFind)
ans = 1
EDU>> EamonnsFindNumber(TeamAges,77)
EDU>> EamonnsFindNumber([66, 77, 45],77)
Let us write a function that takes in an array, a number to find in that array, and returns true/false if the number is in the array
[ 4, 2, 9] 2
EamonnsFindNumber 1

27. function TargetNumberExists = EamonnsFindNumber(ArrayToSearch,TargetNum)
TargetNumberExists = 0; % Assume the number does not exist for now
for i = 1 : length(ArrayToSearch)
if ArrayToSearch(i) == TargetNum
TargetNumberExists = 1; % Change our assumption
end
ArrayToSearch 5 6 11 9 8
EDU>> TeamAges = [ 5 , 6, 11, 9 , 8];
EDU>> AgeToFind = 9;

28. TargetNumberExists = 0; % Assume the number does not exist for now
function TargetNumberExists = EamonnsFindNumber(ArrayToSearch,TargetNum)
TargetNumberExists = 0; % Assume the number does not exist for now
for i = 1 : length(ArrayToSearch)
if ArrayToSearch(i) == TargetNum
disp(['the if statement was triggered with i equals ', num2str(i)])
TargetNumberExists = 1; % Change our assumption
end
Useful hint: It is good idea to add temporary code to echo what is happening in the code.
This is especially true as we consider more complex code
EDU>> EamonnsFindNumber([66, 77, 45],77)
the if statement was triggered with i equals 2
ans = 1

29. Finding Location of Given Number
EDU>> TeamAges = [ 5 , 6, 11, 9 , 8];
EDU>> AgeToFind = 9;
EDU>> FindNumberLocation(TeamAges,AgeToFind)
ans = 4
EDU>> FindNumberLocation(TeamAges,77)
NaN
[ 4, 2, 9] 9
Let us write a function that takes in an array, a number to find in that array, and returns the location of that number in the array.
If the number is not in the array, it return NaN
FindNumberLocation 3

30. Finding Location of Given Number
Important note:
The previous slide did not specify what to do if the target number appears more than once.
It is our job to clarify these things
We could:
Report the first occurrence
Report the second occurrence
Do something else
[ 9, 2, 9] 9
Let us write a function that takes in an array, a number to find in that array, and returns the location of that number in the array.
If the number is not in the array, it return NaN
FindNumberLocation 3

31. NumLocation = NaN; % Assume the number does not exist for now
function NumLocation = FindNumberLocation(ArrayToSearch,TargetNum)
NumLocation = NaN; % Assume the number does not exist for now
for i = 1 : length(ArrayToSearch)
if ArrayToSearch(i) == TargetNum
NumLocation = i; % Assumption was wrong, record the location
end
EDU>> TeamAges = [ 5 , 6, 5, 9 , 7];
EDU>> FindNumberLocation(TeamAges,5)
ans = 3

32. NumLocation = NaN; % Assume the number does not exist for now
function NumLocation = FindNumberLocation(ArrayToSearch,TargetNum)
NumLocation = NaN; % Assume the number does not exist for now
for i = 1 : length(ArrayToSearch)
if ArrayToSearch(i) == TargetNum
NumLocation = i; % Assumption was wrong, record the location
end
Does our code find the first or last occurrence of a number?
It finds the last occurrence
In the next slide we will see how to find the first instead
EDU>> TeamAges = [ 5 , 6, 5, 9 , 7];
EDU>> FindNumberLocation(TeamAges,5)
ans = 3

33. NumLocation = NaN; % Assume the number does not exist for now
function NumLocation = FindNumberLocation(ArrayToSearch,TargetNum)
NumLocation = NaN; % Assume the number does not exist for now
for i = 1 : length(ArrayToSearch)
if ArrayToSearch(i) == TargetNum
NumLocation = i; % Assumption was wrong, record the location
break;
end
The matlab command break terminates a for or while loop.
The moment that Matlab encounters a break it jumps to the end of the loop and continues with the rest of the program…
EDU>> TeamAges = [ 5 , 6, 5, 9 , 7];
EDU>> FindNumberLocation(TeamAges,5)
ans = 1

34. Finding Vowel Count ‘eamonn’ 3
Let us write a function that takes in a string, and returns a count of how many vowels it has.
Let us use our strategy of solving a simpler problem and working our way upto the final solution…
‘eamonn’
Let us use our strategy of echoing to the screen so we can debug the code..
FindVowels 3

35. function VowelCount = FindVowels(StringToSearch)
VowelCount = 0; % Assume there are no vowels
for i = 1 : length(StringToSearch)
if StringToSearch(i) == 'a'
VowelCount = VowelCount + 1;
disp(['An a was found when i was ', num2str(i)])
end
EDU>> FindVowels('eamonn')
An a was found when i was 2
ans = 1
EDU>> FindVowels('abba')
An a was found when i was 1
An a was found when i was 4 2

36. We are not finding uppercase ‘A’
function VowelCount = FindVowels(StringToSearch)
VowelCount = 0; % Assume there are no vowels
for i = 1 : length(StringToSearch)
if StringToSearch(i) == 'a'
VowelCount = VowelCount + 1;
disp(['An a was found when i was ', num2str(i)])
end
There is a bug!
We are not finding uppercase ‘A’
EDU>> FindVowels('ABBA')
ans =

37. There is a simple fix function VowelCount = FindVowels(StringToSearch)
VowelCount = 0; % Assume there are no vowels
for i = 1 : length(StringToSearch)
if lower(StringToSearch(i)) == 'a'
VowelCount = VowelCount + 1;
disp(['An a was found when i was ', num2str(i)])
end
There is a simple fix
EDU>> FindVowels('ABBA')
An a was found when i was 1
An a was found when i was 4
ans = 2

38. We can begin to add more code..
function VowelCount = FindVowels(StringToSearch)
VowelCount = 0; % Assume there are no vowels
for i = 1 : length(StringToSearch)
if lower(StringToSearch(i)) == 'a'
VowelCount = VowelCount + 1;
disp(['An a was found when i was ', num2str(i)])
end
if lower(StringToSearch(i)) == 'e'
disp(['An e was found when i was ', num2str(i)])
EDU>> FindVowels('eamonn')
An e was found when i was 1
An a was found when i was 2
ans = 2
We can begin to add more code..

39. Finding The Largest Value
Let us write a function that finds the largest number in an array.
As it happens, the built in max function does this, but we need to sharpen our skills…
[ ]
EamonnsMax 5

40. 1 4 2 8 function LargestNumber = EamonnsMax(InputArray)
LargestNumber = -Inf; % Assume this is the largest number
for i = 1 : length(InputArray)
if InputArray(i) > LargestNumber
disp('I need to update the largest number')
LargestNumber = InputArray(i);
end
EDU>> EamonnsMax([ ])
I need to update the largest number
ans = 8
EDU>> EamonnsMax([ ]) 4 1 4 2 8