MATLAB-BOOK 🧑🏻‍💻 Class Activities

🧑🏻‍💻 Class Activities 🧑🏻‍💻 Class Activities

These in-class activities focus on writing small MATLAB functions that use if and switch statements. Each activity includes multiple parts and asks you to reason about which branch executes.

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1. Activity 1: Simple `if`-statement.

Use the coding area, below, to complete the following tasks. Each task builds on the previous one, so you can modify your code block as you go.

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(a)

Define the variable x as 6, if use an if-statement to define the variable y according to the following rule:

if x is less than or equal to 9, set y to 1, otherwise set y to 4.

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Solution.

x = 6;

if x <= 9
	y = 1;
else
	y = 4;
end

fprintf('for x = %d, we set y to %d\n', x, y);

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(b)

Change x to 16 and rerun your code block.

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Solution.

Just change the value of x to 16 in the previous code block.

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(c)

Next, define x as a random integer between -5 and 15, using the command randi([-5, 15]).

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Rerun your code multiple times to see how the value of y changes based on the random value of x.

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Solution.

Just change the value of x to randi([-5, 15]) in the previous code block.

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(d)

Update your code to set y according to the following new rule:

if x is between 1 and 9 (inclusive), set y to 1, otherwise set y to 4.

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Solution.

x = randi([-5, 15]);

if x >= 1 & x <= 9
	y = 1;
else
	y = 4;
end

fprintf('for x = %d, we set y to %d\n', x, y);

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2. Activity 2: Updating a Variable with Conditionals.

Use the coding area, below, to complete the following tasks.

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(a)

Suppose num is a random integer between 0 and 20. Give the code that increases num by 5 if it is greater than 10 and decreases it by 5 otherwise.

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Solution.

nnum = randi([0, 20]);
fprintf('Starting num = %d\n', num);

if num > 10
	num = num + 5;
else
	num = num - 5;
end

fprintf('Updated num = %d\n', num);

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(b)

Suppose num is a 1 x 1 double. Give the code that increases num by 5 if it is greater than 10, decreases num by 5 if it is less than 10, and does nothing if num is zero.

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Solution.

If x = 0, the below script runs the commands x = x - 5 and disp(x), outputting -5. However, if x = 10, only the disp(x) command is run, producing an output of 10.

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if x > 10
	x = x + 5;
elseif x < 10
	x = x - 5;
end
disp(x)

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3. Activity 3: Sign Label Function.

Write a function that classifies a single number as positive, negative, or zero.

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(a)

Create a function named sign_label that takes one input x and returns one output label with the value 'positive', 'negative', or 'zero'.

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Solution.

function label = sign_label(x)
	if x > 0
		label = 'positive';
	elseif x < 0
		label = 'negative';
	else
		label = 'zero';
	end
end

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(b)

Modify the function so it returns a second output named code with values 1, -1, or 0 that match the sign.

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Solution.

function [label, code] = sign_label(x)
	if x > 0
		label = 'positive';
		code = 1;
	elseif x < 0
		label = 'negative';
		code = -1;
	else
		label = 'zero';
		code = 0;
	end
end

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4. Activity 4: Freeze Alert Function.

Use a simple if-statement to return a warning message from a temperature input.

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(a)

Write a function named freeze_alert that takes tempC (a scalar temperature in Celsius) and tempWarn (how close to freezing to warn) and returns message. If tempC is at or below tempWarn, return 'Freeze warning'; otherwise return 'No warning'.

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Solution.

function message = freeze_alert(tempC, tempWarn)
	if tempC <= tempWarn
		message = 'Freeze warning';
	else
		message = 'No warning';
	end
end

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(b)

Update the function to return a second output isFreezing that is true or false along with the message.

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Solution.

function [message, isFreezing] = freeze_alert(tempC, tempWarn)
	
	if tempC <= 0
		message = 'Freeze warning';
		isFreezing = true;
	elseif tempC <= tempWarn
		message = 'Freeze warning';
		isFreezing = false;
	else
		message = 'No warning';
		isFreezing = false;
	end
end

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5. Activity 5: Ticket Price Function.

Write a function that uses if-elseif-else to choose among several price brackets.

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(a)

Create a function named ticket_price that takes a scalar input age (a single person’s age, in years) and returns price using the rules below:

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Age less than 13: price = 6

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Age from 13 to 64: price = 12

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Age 65 or older: price = 8

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(b)

Modify the function so it returns a second output group and handles invalid ages. If age < 0, return price = NaN and group = 'invalid'.

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6. Activity 6: Letter Grade Function.

Convert a numeric score to a letter grade using range-based conditions.

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(a)

Write a function named letter_grade that returns 'A', 'B', 'C', 'D', or 'F' for a scalar score using the standard 90/80/70/60 cutoffs.

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(b)

Add an input check so that scores outside 0 to 100 return 'invalid'.

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(c)

Concept check: why must the score >= 90 test appear before the score >= 80 test?

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7. Activity 7: Shipping Mode Switch.

Use a switch statement to choose among discrete shipping options.

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(a)

Create a function named shipping_cost that takes a mode input ('S', 'E', or 'O') and returns a scalar cost of 5, 12, or 20.

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Solution.

function cost = shipping_cost(mode)
	switch mode
		case 'S'
			cost = 5;
		case 'E'
			cost = 12;
		case 'O'
			cost = 20;
		otherwise
			cost = NaN;
	end
end

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(b)

Extend the function so it also accepts full words ('standard', 'express', and 'overnight') in addition to the single-letter codes.

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Solution.

function cost = shipping_cost(mode)
	switch mode
		case {'S', 'standard'}
			cost = 5;
		case {'E', 'express'}
			cost = 12;
		case {'O', 'overnight'}
			cost = 20;
		otherwise
			cost = NaN;
	end
end

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(c)

Concept check: what happens when mode = 'e' (lowercase), and why?

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Solution.

The otherwise branch runs and returns NaN because switch comparisons are case-sensitive, so 'e' does not match 'E'.

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8. Activity 8: Day Type Switch.

Map a day number to weekday or weekend status using a switch-statement.

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(a)

Write a function named day_type that takes an integer dayNum (1 = Monday, 7 = Sunday). Return 'weekday' for 1--5 and 'weekend' for 6--7.

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(b)

Update the function to return a second output named isWeekend that is true or false for valid days.

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(c)

Concept check: what should the function return for dayNum = 0, and which branch handles it?

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9. Activity 9: Thermostat Mode Switch.

Use a discrete numeric code to select a thermostat mode.

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(a)

Create a function named thermostat_mode that takes a numeric code: 0 for off, 1 for heat, and 2 for cool. Return the string 'off', 'heat', or 'cool'.

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(b)

Extend the function to return a second output setPoint. Use 68 for heat, 74 for cool, and NaN for off or invalid codes.

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10. Activity 10: Late Fee Function.

Use an if-elseif-else chain to assign a fee based on how late something is.

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(a)

Write a function named late_fee that takes a single number daysLate (the number of days late) and returns fee according to the table below:

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`daysLate`	`fee`
0 or less	0
1 to 3	5
3 to 7	15
\(\quad\) more than 7\(\quad\)	\(\quad\)30\(\quad\)

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(b)

Modify the function to return a second output status with values according to the table below:

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`daysLate`	`fee`	`status`
0 or less	0	on time
1 to 3	5	minor late
3 to 7	15	late
\(\quad\) more than 7\(\quad\)	\(\quad\)30\(\quad\)	\(\quad\)very late\(\quad\)

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🧑🏻‍💻 Class Activities 🧑🏻‍💻 Class Activities

1. Activity 1: Simple if-statement.

(a)

(b)

(c)

(d)

2. Activity 2: Updating a Variable with Conditionals.

(a)

(b)

3. Activity 3: Sign Label Function.

(a)

(b)

4. Activity 4: Freeze Alert Function.

(a)

(b)

5. Activity 5: Ticket Price Function.

(a)

(b)

6. Activity 6: Letter Grade Function.

(a)

(b)

(c)

7. Activity 7: Shipping Mode Switch.

(a)

(b)

(c)

8. Activity 8: Day Type Switch.

(a)

(b)

(c)

9. Activity 9: Thermostat Mode Switch.

(a)

(b)

10. Activity 10: Late Fee Function.

(a)

(b)

1. Activity 1: Simple `if`-statement.