1. Loops & More 1.Conditionals (review) 2.Running totals and Running products 3.the for loop, examples 4.Nesting for loops, examples 5.Common errors 1

2. Ex4, algorithm Ask user for a list of surfaces in meters squared. Add all surfaces together. Stop asking when a negative/or null surface is entered! % start result at zero % get the first surface % As long as the current surface is positive % “running total”: add surface to total % ask for next surface value % display total surface to the screen 2

3. Ex4, initialization % start result at zero sumSurfaces = 0; % prompt for a surface (and give directions) % As long as surface is positive % “running total”: add surfaces as they are given % ask for next surface value % display total surface to the screen 3

4. Ex4, initialization % start result at zero sumSurfaces = 0; % prompt for a surface (and give directions) fprintf('Note: a negative/zero surface quits.\n'); surface = input('Enter surface (m^2): '); % As long as surface is positive % “running total”: add surfaces as they are given % ask for next surface value % display total surface to the screen 4

5. Ex4, block of code %start result at zero sumSurfaces = 0; % prompt for a surface (and give directions) fprintf('Note: a negative/zero surface quits.\n'); surface = input('Enter surface (m^2): '); % As long as surface is positive % “running total”: add surfaces as they are given sumSurfaces = sumSurfaces + surface; % ask for next surface value % display total surface to the screen 5

6. Ex4, change of condition %start result at zero sumSurfaces = 0; % prompt for a surface (and give directions) fprintf('Note: a negative/zero surface quits.\n'); surface = input('Enter surface (m^2): '); % As long as surface is positive % “running total”: add surfaces as they are given sumSurfaces = sumSurfaces + surface; % ask for next surface value surface = input('Next surface: '); % display total surface to the screen 6

7. Ex4, fill in the code %start result at zero sumSurfaces = 0; % prompt for a surface (and give directions) fprintf('Note: a negative/zero surface quits.\n'); surface = input('Enter surface (m^2): '); % As long as surface is positive while % “running total”: add surfaces as they are given sumSurfaces = sumSurfaces + surface; % ask for next surface value surface = input('Next surface: '); end % display total surface to the screen 7

8. Ex4, condition %start result at zero sumSurfaces = 0; % prompt for a surface (and give directions) fprintf('Note: a negative/zero surface quits.\n'); surface = input('Enter surface (m^2): '); % As long as surface is positive while surface>0 % “running total”: add surfaces as they are given sumSurfaces = sumSurfaces + surface; % ask for next surface value surface = input('Next surface: '); end % display total surface to the screen 8

9. Ex4, continue %start result at zero sumSurfaces = 0; % prompt for a surface (and give directions) fprintf('Note: a negative/zero surface quits.\n'); surface = input('Enter surface (m^2): '); % As long as surface is positive while surface>0 % “running total”: add surfaces as they are given sumSurfaces = sumSurfaces + surface; % ask for next surface value surface = input('Next surface: '); end % display total surface to the screen fprintf('All surfaces add up to %.4f m^2.\n', sumSurfaces); 9

10. Ex4, output result 10

11. 1. while (review) while is used to – repeat an unknown amount of time trap the user while invalid data is entered prompt the user for an unknown amount of values Give limited/unlimited attempts to username/password checks Overall syntax: initialize while condition(s) body of code, which MUST include a statement that updates the T/F status of the condition end 11 1 2 3 4 5 6

12. 1. this while loop is complete 12 % prompt for a surface (and give directions) fprintf(‘Note: a negative/zero surface quits.\n’); surface = input(‘Enter surface (m2): ’); sumSurfaces = 0; %start result at zero % while surface is positive (i.e. valid) while surface>0 % keep track of sum sumSurfaces = sumSurfaces + surface; % ask for next surface value surface = input(‘Next surface: ’); end % display total surface to the screen fprintf(‘These %d surfaces add up to %.4f m2.\n’, nbSurfaces, sumSurfaces); Initialize (starting point) condition (continuing(true) point / stopping(false) point) updating the variable involved in the condition

13. 2. Running totals (review) mytotal = mytotal + newScore; 13 “Add as you go…” 3058 mytotal 8 newScore 3066

14. 2. Running totals (review) mytotal = 14 “Count as you go…” 3058 mytotal 8 newScore 3066

15. 2. Running totals (review) mytotal = mytotal + newScore; 15 “Count as you go…” 3066 mytotal 8 newScore ?

16. 2. Running totals (review) Applications of running total – sum values as they are entered – count values when they satisfy a criteria – count values when they do NOT satisfy a criteria – … ALWAYS initialize your variable (more than likely at 0, but not necessarily!) 16

17. Add the surfaces as you go… 17 % prompt for a surface (and give directions) fprintf(‘Note: a negative/zero surface quits.\n’); surface = input(‘Enter surface (m2): ’); sumSurfaces = 0; %start result at zero % while surface is positive (i.e. valid) while surface>0 % keep track of sum sumSurfaces = sumSurfaces + surface; % ask for next surface value surface = input(‘Next surface: ’); end % display total surface to the screen fprintf(‘These %d surfaces add up to %.4f m2.\n’, nbSurfaces, sumSurfaces);

18. Add a counter for nb of surfaces 18 % prompt for a surface (and give directions) fprintf(‘Note: a negative/zero surface quits.\n’); surface = input(‘Enter surface (m2): ’); sumSurfaces = 0; %start result at zero % while surface is positive (i.e. valid) while surface>0 % keep track of sum sumSurfaces = sumSurfaces + surface; % ask for next surface value surface = input(‘Next surface: ’); end % display total surface to the screen fprintf(‘These %d surfaces add up to %.4f m2.\n’, nbSurfaces, sumSurfaces); ?

19. 2. Running Products Running total implies a “sum” Running “products”: result = result * newValue; You can even combine running totals and running products: %sum the volumes result = result + length*width*height; Make sure this is inside a loop! 19

20. 3. Another type of loop Matlab has two loops, one for each method explained previously: while – Generic, all-purpose. Best used when the programmer does not know how many times the block of code needs to repeat. – Repeats while a CONDITION is true. for – A COUNTING loop. Best used when the programmer “knows” how many times the block of code needs to repeat. 20

21. 3. for statement >> doc for for Execute statements a specified number of times Syntax for index = initval:step:endval program statements; end 21 initval:endval increments the index variable from initval to endval by +1, and repeats execution of program statements until index is greater than endval. initval:step:endval increments index by the value step on each iteration, or decrements when step is negative.

22. while vs. for mySum = 0; x = 1; while x<=10 mySum = mySum + x; x = x +1; end fprintf(‘Sum: %d.\n’, mySum); 22 For example, this loop counts from 1 to 10, by steps of +1 mySum = 0; for x = 1:10 mySum = mySum + x; end fprintf(‘Sum: %d.\n’, mySum); 1 2 3 4 5 6 7 1234512345 The range-operator ( : )

23. while vs. for : initialize (1) mySum = 0; x = 1; while x<=10 mySum = mySum + x; x = x +1; end fprintf(‘Sum: %d.\n’, mySum); 23 Both loops initialize mySum = 0; for x = 1:10 mySum = mySum + x; end fprintf(‘Sum: %d.\n’, mySum); 12345671234567 1234512345

24. while vs. for : condition (2) mySum = 0; x = 1; while x<=10 mySum = mySum + x; x = x +1; end fprintf(‘Sum: %d.\n’, mySum); 24 Both loops have a point where to stop mySum = 0; for x = 1:10 mySum = mySum + x; end fprintf(‘Sum: %d.\n’, mySum); 12345671234567 1234512345

25. while vs. for : code to repeat (3) mySum = 0; x = 1; while x<=10 mySum = mySum + x; x = x+1; end fprintf(‘Sum: %d.\n’, mySum); 25 Both loops repeat a statement mySum = 0; for x = 1:10 mySum = mySum + x; end fprintf(‘Sum: %d.\n’, mySum); 12345671234567 1234512345

26. while vs. for : update loop-variable (4) mySum = 0; x = 1; while x<=10 mySum = mySum + x; x = x+1; end fprintf(‘Sum: %d.\n’, mySum); 26 Both loop increase by +1 mySum = 0; for x = 1:10 mySum = mySum + x; end fprintf(‘Sum: %d.\n’, mySum); 12345671234567 1234512345 the default is +1

27. The for is a “counting” loop mySum = 0; x = 1; while x<=10 mySum = mySum + x; x = x+1; end fprintf(‘Sum: %d.\n’, mySum); 27 for - initialize, increment and condition are together mySum = 0; for x = 1:10 mySum = mySum + x; end fprintf(‘Sum: %d.\n’, mySum); 12345671234567 1234512345 the default is +1 The for loop is a “counting loop”

28. Loop “Unrolling” mySum = 0; x = 1; mySum = mySum + x; x = 2; mySum = mySum + x; x = 3; mySum = mySum + x; x = 4; mySum = mySum + x; x = 5; mySum = mySum + x; x = 6; mySum = mySum + x; x = 7; mySum = mySum + x; x = 8; mySum = mySum + x; x = 9; mySum = mySum + x; x = 10; mySum = mySum + x; fprintf('Sum: %d\n', mySum); 28 mySum = 0; for x = 1:10 mySum = mySum + x; end fprintf(‘Sum: %d.\n’, mySum);

29. Updating the surfaces… % prompt the user how many surfaces, check valid while end %loop that many times for %prompt for that surface %add the surfaces as we go end %indicate the total surface 29

30. Be friendlier to the user From this: To this: 30

31. CAUTION/HINTS input() does NOT work with placeholders. input() is meant to prompt the user for data, NOT to format an output. 31

32. Using an increment different than +1 32 Perfect for single countdowns! – In countdowns, the increment is _____. initval:step:endval increments index by the value step on each iteration, or decrements when step is negative. Any ideas? – keywords to use? – which loop(s)? – possible issues?

33. Example2: Thrust of a rocket Rockets can have multiple engines. Each engine can have a different thrust. The user will chose how many engines, though MATLAB will generate all the numbers for a possible rocket design scenario. 33

34. Example2: Thrust of a rocket Step2: Assume 3 pairs (6 total) engines (fired at different times maybe..) Step3: TotalThrust = 2* sum of thrust per engine Step4: -For stability purposes, assume the number of engines needs to be even, and the thrusts go by 2. -Range of an engine thrust will be between 20 000lbs and 100 000lbs. 34

35. Example2: Thrust of a rocket Step5: Assume 6 engines, with the following generated by MATLAB: engines1: 25 000 lbs engines2:55 000 lbs engines3:98 000 lbs total thrust = 2*(25+55+98)*1000 = 356 000 lbs Step6 35

36. Algorithm %prompt the user the amount of engines, check valid %start sum at zero %loop half that many times for %generate/display the thrust (rand) %sum up the thrusts end %calculate/display final thrust for the rocket 36

37. Possible Output #1 37

38. Possible Output #2 38

39. Common errors Decrement.. (But not really) for k = 10:1 fprintf(‘%d\n’,k); end Changing the loop variable within the for loop (or trying to..) for k = 1:2:5 fprintf(‘%d\n’,k); k = k+1; %a remain of the while loop??? end 39 Incremement by +2 or by +1 ??? What choice will MATLAB make?

40. Common errors Counting.. (But not really) for 1:10 fprintf(‘hi\n’); end 40

41. Key ideas The for loop is a counting loop The while loop can always be used BUT…the for loop is meant to count – The startvalue:step:endValue contains all necessary values for the loop to work. Nested for loops are absolutely possible! Actually, any construct ( if, switch, while, for ) can now be nested within each other. 41