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Loops & More

WHILE loops

FOR loopsRange operatorRunning totals

Random Numbers

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Review• Review while loops

while (time < 3.15)

• Review infinite loop while (true)

• Introduce for loop for x = 1:10

• Introduce range operator x=1:10 or x=1:2:10

• Sum elements in a loop

• Compute average of values

• Get min/max values from a loop

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WHILE Loop - Review

• Generally you have a loop control variable This variable has 3 phases

• Initialization of variable• Change of variable• Condition to continue running the loop

• Example: the loop control variable is xx = 0; 1. initialization

while ( x < 10) 2. condition

x = x + 1; 3. change loop variable

fprintf('%02d\n', x);

end

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Loops Review

• Infinite Loop The loop condition never becomes false and the loop runs, and runs…

• Use CTRL-C in the command window to break it (or alt-F4 if infinite loop with dialog boxes)

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Loop Review

Why is this an infinite loop in MATLAB?

x = 9; % 1. initialization

while ( x > 10) % 2. condition

fprintf('%02d\n', x);

x = x + 1; % 3. change loop variable

end

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Trap a user for a value

• Ask a user for a value between 1 to 10

• What if they don't give the proper value?

Two approaches:– Ask first, then loop– Make bad and loop

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Validate input, cont.

Ask first, then loop:

numValues = input('Value from 1-10: '); % ask first

while (numValues<1 || numValues>10) numValues = input('Error! Enter a value 1-10:

');end

Make bad, then loop:numValues = -1; % makes loop run at least oncewhile (numValues<1 || numValues>10)

numValues = input('Value from 1-10: ');end

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FOR Loop

• Generally used for a fixed number of iterations• You know you want to go from 1 to 100, by ones• for syntax does all 3 parts of the loop in one line

initialization, change, condition

for k = 1:100disp(k);

end

The symbol : is a new operator, it's the range operator. The range is from 1 to 100, by ones. We say “in steps of one”

If you want to loop in steps of 2, use 1:2:100

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Range Operator [:]

• for loops use the range operator to specify a range of values to loop over (to iterate)

• Syntax:

variable = start : increment : end

: increment is optional

– defaults to : 1 if omitted

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Range Operator, cont.

Examples:

(in all examples, there is an implied loop body and end)

% loop 10 times

for x = 1:10

% It is not necessary that the values be integers

for y = 1.2 : 2.3 : 100.5

% Can use negative steps

for z = 10:-2:1

So… when does it stop?

Steps of -2 will never “hit” the value of 1…

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Range Operator, cont.

The loop continues as long as the value is “in the range” specified

for ctr=1:3:10 % as long as 1 <= ctr <= 10

for val=-5:2:5 % as long as -5 <= val <= 5

for thing=5:-3:0 % as long as 5 >= thing >= 0

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FOR loops, cont.

Which brings up a very important issue:

It is possible to change the loop counter while in the body of a FOR loop

This is normally not a good idea since the value will revert back in the next loop iteration

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FOR loops, cont.for cnt=1:5

fprintf('%d\n', cnt);

cnt = cnt * 2;

end

Output:1

2

3

4

5

>>

Notice that the variable changed back at the top of the loop

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Nested FOR loopsGenerate a table of output that looks like a clock for every

second of the day

for hr= 0:23 % all hours for dayfor min = 0:59 % all minutes per hour

for sec = 0:5:59 % all seconds per min per hour

fprintf('%02d:%02d:%02d\n', hr, min, sec);

endend

end

Test the Code!

Write a program that prints all days of the year for the decade, Year, Month, Days

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Loops: Running Totals / Running Products

• Loops are useful for accumulating or summing values..computing averages, totals etc. (“running totals”, “running products”)

• Running total:– Start with a variable for the sum initialized to 0

sum = 0;

– Each time through loop add a value to the sum: sum = sum + number;

• Running product:– Start with a variable for the product, initialized to 1

prod = 1;

– Each time through loop, multiply: prod = prod * number;

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Loops: Running total

% initialize valuestotal = 0;value = 0;

%loop when value positive or zerowhile value >=0

fprintf('Negative values quit…\n')value = input('Enter a positive integer: ');if value >=0 %add value if positive

total = total + value ;end % of if

end % of while

%display resultfprintf('total = %d\n', total);

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Loops: Compute Average

1. Initialize sum before the loop sum = 0;

2. Keep a running total in the loop:sum = sum + number;

3. After loop, divide by countaverage = sum /

iterations;

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FOR Loop: Average

• Generate 10 random values between 0 and 1 then compute average

%initialize variablessum = 0;average = 0;

%loop 10 timesfor x = 1:10

value = rand; %generate 1 random value ]0-1[fprintf('value %02d is %.3f\n', x, value);sum = sum + value;

end

%calculate, display averageaverage = sum / 10; fprintf ('the average is %.3f\n', average);

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Output results

Second run:

value 01 is 0.971value 02 is 0.957value 03 is 0.485value 04 is 0.800value 05 is 0.142value 06 is 0.422value 07 is 0.916value 08 is 0.792value 09 is 0.959value 10 is 0.656The average is 0.710

First run:

value 01 is 0.906value 02 is 0.127value 03 is 0.913value 04 is 0.632value 05 is 0.098value 06 is 0.278value 07 is 0.547value 08 is 0.958value 09 is 0.965value 10 is 0.158The average is 0.558

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FOR Loop: Roll Dice 10 times• Combine the for loop, with ceil,

and rand

%loop 10 times

for x = 1:10

%generate a die rolldice = ceil(rand*6);

%display

fprintf('roll %d is %d\n', x, dice);

end

roll 1 is 1roll 2 is 6roll 3 is 6roll 4 is 5roll 5 is 5roll 6 is 5roll 7 is 3roll 8 is 4roll 9 is 2roll 10 is 5

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Loops: Find Min / Max• Trying to find a min value or max value

• First time through the loop, set the minimum and the maximum value to the number.

if (count == 1)min = number;max = number;

end

• Each subsequent time, determine if number is greater than maximum if so, change maximum to contain this new biggest value

if (number > max) max = number;end

There are also functions min() and max() – we will use them later with vectors & arrays

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Loops: Find Min / MaxN = input('How many values? ');

for count=1:Nnumber = input('Please give me a number: ');

if count==1min_val = number;max_val = number;

end % of if

if number > max_valmax_val = number;

end

if number < min_valmin_val = number;

end

end % of for

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Taboos

http://www.egr115.com/taboos.pdf

Don't use these words in your programs:

• global

• persistent

• break

• continue

• error

• exit

• quit

MAJOR points lost for using these in your programs!

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Combine FOR / rand() / mod()

• Write a program that picks 200 random integers between 1 .. 100

• Determine how many are odd and how many are even

• Print out the # of odd values, # even values, and compute the percentages of odd and even values

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An algorithmfor ???

pick rand numberif odd

Increment odd counterelse

Increment even counterend

end

% Compute odd percentage% Compute even percentage% Print out results

Note counters need to be INITIALIZED to 0.

Before or in the loop?

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Solution% set up countersodd_cnt = 0;even_cnt = 0;

%loop to create/analyze numbersfor cnt=1:200

value = floor(rand()*100) + 1;if mod(value, 2) == 1 % odd number

odd_cnt = odd_cnt + 1;else % even number

even_cnt = even_cnt + 1;end

end

%calculate/display resultsodd_pct = 100* odd_cnt / 200;even_pct = 100 * even_cnt / 200;fprintf('%.2f%% were odd,', odd_pct);fprintf('and %.2f%% were even\n', even_pct);

Notice the lack of semicolons (;) in FOR and IF statements

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How long to generate random #'s

• Write a program that generates random numbers from 1 – 100

• Keep running program 'til every number gets one occurrence. That's an array problem, have to do that in a week or so…

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Final ProjectIntroduction

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Final Project

The descriptions provided here are only acting as summaries – please see the complete description on your section's website.

Goal

Create a project of your choosing within the constraints specified by your instructor. The goal of your project is to logically implement as many of the semester topics as possible, consistent with your project's purpose.

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Final Project, cont.

While all topics contribute to the grading of the project, heavy emphasis is assigned to the proper use of:

• Algorithm• Complexity and efficiency• Programmer-defined functions• Loops• File I/O

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Final Project, cont.

•Connect 4•Hunting Database•MP3 player•Keyboard DDR•Drum Hero•Will a beam break?•Fuel efficiency and gas cost•Ball and wall collision•Automatic toll system•Forces in a car crash•Electrical circuit analysis

Examples of past projects:•Audio Analysis•Serial Port IM•Thermistor Data Collection•Bezier Curve Fit•Unit Conversion•Tournament Generation•Deal or No Deal•Load and moment distribution on a beam w/ plotting•Captain's Jack Sparrow'smagical compass

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Final Project, cont.

Possible areas for new projects:

GenealogyThermodynamicsComputational Fluid DynamicsImage / Visual ProcessingModel Rocket / RC Plane Telemetry2D / 3D environment modelingOrbital Mechanics

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Final Project, cont.

Extra Credit is provided for:

• Innovative project concepts

• Advanced programming techniques

• Exceptional program development

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Final Project, cont.

Today is Tuesday October 2, 2012

Projects will be due around December 5.

This gives you about 8 weeks.- One week to pick a topic- Two weeks to plan and modify your design- Five weeks to code, revise, and test

Past students have quoted about 30 hours dedicated to the project. If we assume virtually all of that was coding, you can plan on spending 6 hours per week on the coding portion – IF you give yourself enough time.

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Final Project, cont.

Begin planning!

- Find an idea: what interests you?

- Discuss with your instructor

- Layout a plan for what it will entail

- You should be coding by Oct. 22!

- If you start early, there is time to revise