If-elseif-else statements in MATLAB - Mini Project: Build & Apply

If-elseif-else statements

📖 Scenario: You are creating a simple program to check the temperature and give advice on what to wear.

🎯 Goal: Build a MATLAB script that uses if-elseif-else statements to print clothing advice based on the temperature.

📋 What You'll Learn

Create a variable temperature with a specific value

Create a variable cold_threshold with a specific value

Use if-elseif-else statements to check the temperature against thresholds

Print the correct advice message based on the temperature

💡 Why This Matters

🌍 Real World

Checking temperature and giving clothing advice is common in weather apps and daily planning tools.

💼 Career

Understanding conditional statements is essential for programming logic in many software development jobs.

1

DATA SETUP: Create the temperature variable

Create a variable called temperature and set it to 15.

MATLAB

temperature = 0; % Your code here

Hint

Use the assignment operator = to set temperature to 15.

2

CONFIGURATION: Create the cold threshold variable

Create a variable called cold_threshold and set it to 10.

MATLAB

temperature = 15;
cold_threshold = 0; % Your code here

Hint

Set cold_threshold to 10 using the assignment operator.

3

CORE LOGIC: Use if-elseif-else to check temperature

Write an if-elseif-else statement that checks if temperature is less than cold_threshold. If yes, assign advice the value 'Wear a coat.'. Else if temperature is less than 20, assign advice the value 'Wear a jacket.'. Otherwise, assign advice the value 'Wear a t-shirt.'.

MATLAB

temperature = 15;
cold_threshold = 10;
% Your code here

Hint

Use if, elseif, and else keywords with conditions and assign advice accordingly.

4

OUTPUT: Display the advice

Use disp to print the value of the variable advice.

MATLAB

temperature = 15;
cold_threshold = 10;

if temperature < cold_threshold
    advice = 'Wear a coat.';
elseif temperature < 20
    advice = 'Wear a jacket.';
else
    advice = 'Wear a t-shirt.';
end
% Your code here

Hint

Use disp(advice) to show the advice on the screen.

Practice

1. What does an if-elseif-else statement do in MATLAB?

easy

A. It creates a variable.

B. It repeats a block of code multiple times.

C. It defines a function.

D. It chooses one action based on conditions.

Solution

1. Step 1: Understand the purpose of if-elseif-else

   The if-elseif-else structure lets the program check conditions one by one and run the code for the first true condition.

2. Step 2: Compare with other options

   Repeating code is done by loops, functions define reusable code, and variables store data, so these are not correct.

3. Final Answer:

   It chooses one action based on conditions. -> Option D

4. Quick Check:

   If-elseif-else = choose action [OK]

Hint: If you see conditions, think if-elseif-else [OK]

Common Mistakes:

• Confusing if-elseif-else with loops
• Thinking it defines functions
• Believing it creates variables

2. Which of the following is the correct syntax to start an if-elseif-else block in MATLAB?

easy

A. if x > 0
elseif x == 0
else
end

B. if x > 0 elseif x == 0 else end

C. if (x > 0) then elseif (x == 0) else end

D. if x > 0; elseif x == 0; else; end

Solution

1. Step 1: Check MATLAB syntax rules

   MATLAB requires each keyword (if, elseif, else, end) on its own line or separated by line breaks, without 'then'.

2. Step 2: Analyze each option

   if x > 0 elseif x == 0 else end uses line breaks correctly. if x > 0 elseif x == 0 else end misses line breaks. if (x > 0) then elseif (x == 0) else end uses 'then' which is invalid. if x > 0; elseif x == 0; else; end uses semicolons incorrectly in control flow.

3. Final Answer:

   if x > 0 elseif x == 0 else end -> Option A

4. Quick Check:

   MATLAB if-elseif-else needs line breaks [OK]

Hint: Use line breaks, no 'then' in MATLAB if statements [OK]

Common Mistakes:

• Using 'then' keyword
• Putting all keywords on one line without breaks
• Using semicolons after if/elseif/else

3. What will be the output of this MATLAB code?

score = 75;
if score >= 90
    grade = 'A';
elseif score >= 80
    grade = 'B';
elseif score >= 70
    grade = 'C';
else
    grade = 'F';
end
disp(grade)

medium

A. C

B. B

C. A

D. F

Solution

1. Step 1: Check conditions in order

   score is 75, first condition score >= 90 is false, second score >= 80 is false, third score >= 70 is true.

2. Step 2: Assign grade and display

   Since third condition is true, grade = 'C' is assigned and displayed.

3. Final Answer:

   C -> Option A

4. Quick Check:

   75 >= 70 -> grade C [OK]

Hint: Check conditions top to bottom, first true wins [OK]

Common Mistakes:

• Choosing grade B or A incorrectly
• Ignoring order of conditions
• Forgetting to use end to close if block

4. Identify the error in this MATLAB code snippet:

value = 10;
if value > 5
    disp('Greater than 5')
elseif value < 5
    disp('Less than 5')
else
    disp('Equal to 5')

medium

A. Missing semicolon after disp statements

B. Missing end to close the if block

C. Incorrect use of elseif instead of else if

D. Using single quotes instead of double quotes

Solution

1. Step 1: Check if block completeness

   The if-elseif-else block must end with an end keyword in MATLAB to close it properly.

2. Step 2: Verify other syntax elements

   Semicolons after disp are optional, elseif is correct keyword, and single quotes are correct for strings in MATLAB.

3. Final Answer:

   Missing end to close the if block -> Option B

4. Quick Check:

   if blocks need end [OK]

Hint: Always close if with end [OK]

Common Mistakes:

• Forgetting end keyword
• Confusing elseif with else if
• Thinking semicolons are mandatory after disp

5. You want to write a MATLAB function that returns:
- 'Positive' if input > 0
- 'Zero' if input == 0
- 'Negative' if input < 0
Which if-elseif-else structure correctly implements this?

hard

A. if x > 0
result = 'Positive';
else if x == 0
result = 'Zero';
else
result = 'Negative';
end

B. if x >= 0
result = 'Positive';
elseif x == 0
result = 'Zero';
else
result = 'Negative';
end

C. if x > 0
result = 'Positive';
elseif x == 0
result = 'Zero';
else
result = 'Negative';
end

D. if x > 0
result = 'Positive';
elseif x > 0
result = 'Zero';
else
result = 'Negative';
end

Solution

1. Step 1: Check condition order and correctness

   if x > 0 result = 'Positive'; elseif x == 0 result = 'Zero'; else result = 'Negative'; end correctly checks x > 0 first, then x == 0, else negative. This covers all cases without overlap.

2. Step 2: Analyze other options for errors

   if x >= 0 result = 'Positive'; elseif x == 0 result = 'Zero'; else result = 'Negative'; end wrongly treats x == 0 as Positive. if x > 0 result = 'Positive'; else if x == 0 result = 'Zero'; else result = 'Negative'; end uses invalid 'else if' instead of 'elseif'. if x > 0 result = 'Positive'; elseif x > 0 result = 'Zero'; else result = 'Negative'; end repeats x > 0 condition twice, missing zero case.

3. Final Answer:

   if x > 0 result = 'Positive'; elseif x == 0 result = 'Zero'; else result = 'Negative'; end -> Option C

4. Quick Check:

   Check conditions in order, use elseif [OK]

Hint: Use elseif, not else if; order conditions carefully [OK]

Common Mistakes:

• Using else if instead of elseif
• Overlapping conditions
• Wrong order causing incorrect results