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General Computer Science for Engineers CISC 106 Midterm 2 Review

General Computer Science for Engineers CISC 106 Midterm 2 Review. James Atlas Computer and Information Sciences 11/06/2009. Important Notes on Exam. Write code Study labs + project Study Midterm review. Switch construct. color = ‘yellow’; switch ( color ) case ‘red’

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General Computer Science for Engineers CISC 106 Midterm 2 Review

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  1. General Computer Science for EngineersCISC 106Midterm 2 Review James Atlas Computer and Information Sciences 11/06/2009

  2. Important Notes on Exam Write code Study labs + project Study Midterm review

  3. Switch construct color = ‘yellow’; switch (color) case ‘red’ disp(‘Stop now!’); case ‘green’ disp(‘Proceed through intersection.’); case ‘yellow’ disp(‘Prepare to stop.’); otherwise disp(‘Illegal color encountered.’); end

  4. Logical Operators • &, && - AND • |, || - OR • ~ - NOT

  5. Array commands • a = [1 2 3 4 5] • b = [1; 2; 3; 4] • c = [1 2; 3] (error) • d = [1 2; 3 4] • f = d(1,2) • g(4,5) = 7 • a(3:end) • a(1:2:end) • d’

  6. For Loops • Used when you know how many times code is to be executed. • Syntax for <variable> = <start>:<increment>:<end> • Variable is initially the start value • At end of iteration variable changes by increment • If value is not greater than end the loop runs again.

  7. Example Problem • total = 0; for i = 1:1:1000 loop starts at 1 total = total + i; loop increments by 1 end loop ends at 1000 disp(total);

  8. A Loop Analogy (for) • The runner executes a loop. • If they know the distance they want to run • For loop for lapCount = start : 1 : end runLap() end

  9. A Loop Analogy (while) • The runner executes a loop. • If they don’t know the distance they want to run (run until tired) • While loop tired = false; while(~tired) tired = runLap() end

  10. Linear Search • Given [5 4 2 10 6 7] find which position 6 occupies • Alternatively, does the array contain the number 6? foundIndex = -1; for index = 1:length(values) if (values(index) == 6) foundIndex = index; end end

  11. Binary Search • Now, what if the array is sorted, can we search it faster?

  12. Binary Search • Find N in list • Pick a number X halfway between the start and end of the list • If X == N we are done else if X < N search top half of list else search bottom half of list

  13. Algorithm for sorting (Selection Sort) • Find the minimum data in the set • Swap it with the first element of the set • Repeat Steps 1-2 for the remaining elements

  14. Running Time (Selection Sort) loop progress

  15. Algorithm for sorting (Quick Sort) • Choose a random pivot point • Split your data into two sets: • Low - the data < pivot • High - the data > pivot • Repeat Steps 1-2 for both data sets • The sorted data is [low pivot high]

  16. Running Time (Quick Sort) recursion progress If we divide the size of the data, n, in half at each step, how many steps does this take? log n area of table = width * height = n * log n

  17. Structures in MATLAB

  18. A Database Application • Given: Name: Chris Credits: 27 Graduation: 12/15/2011 Name: Sola Credits: 18 Graduation: 05/17/2011 Name: Roger Credits: 55 Graduation: 06/10/2009 Name: Tom Credits: 15 Graduation: 05/22/2012

  19. A Database Application Name: Chris Credits: 27 Graduation: 12/15/2011 Chris 27 12/15/2011 Name: Sola Credits: 18 Graduation: 05/17/2011 Sola 18 05/17/2011 Roger 55 06/10/2009 Name: Roger Credits: 55 Graduation: 06/10/2009 Tom 15 05/22/2012 Name: Tom Credits: 15 Graduation: 05/22/2012 Given: We can implement it with arrays like this: Name Credits Grad. 1 2 3 4

  20. A Database Application Name: Chris Credits: 27 Graduation: 12/15/2011 Students (1). Name: Chris Students (1).Credits: 27 Students (1). Graduation: 12/15/2011 Name: Sola Credits: 18 Graduation: 05/17/2011 Students (2).Name: Sola Students (2).Credits: 18 Students (2).Graduation: 05/17/2011 Name: Roger Credits: 55 Graduation: 06/10/2009 Students (3). Name: Roger Students (3). Credits: 55 Students (3). Graduation: 06/10/2009 Name: Tom Credits: 15 Graduation: 05/22/2012 Students (4). Name: Tom Students (4). Credits: 15 Students (4). Graduation: 05/22/2012 Given: OR we can do it like this an array with structs: .d

  21. MATLAB Array Initialization y = []; for i = 1:10 y(i) = i; end; This is an example of “growing” an array

  22. MATLAB Array Initialization y = zeros(1,10); for i = 1:10 y(i) = i; end; Initializes the array first

  23. Vectorization • Additional examples • x = [1 2 3 4 5 6]; • x < 3 • x(x < 3) • x(x < 3 | x > 3) • x < 3 produces a mask

  24. Masking • Masking selects only certain elements of an array to perform an operation • Masking uses an array of only 0’s and 1’s that is the same size as the argument • y = x < 3 • whos y • y is a mask of x that selects only the elements that are less than 3

  25. Masking • x = [1 2 3 4 5 6]; • y = x < 3 • x(y) = x(y) .* 2;

  26. MATLAB functions - find • find • locates index of all nonzero elements of array • z = [5 3 0 0 0 7]; • find(z) • [1 2 6]

  27. MATLAB functions - any/all • x = [1 2 3 4 5 6]; • any(x < 3) • any(x < 0) • all(x > 1) • all(x > 0)

  28. MATLAB functions - randi • rand() • randi(100)

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