First MATLAB program - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a simple MATLAB script

What is the output of this MATLAB code when run in the command window?

MATLAB

x = 5;
y = 3;
z = x + y;
disp(z);

A x + y

B 8

C 53

D Error: Undefined function or variable 'z'.

💡 Hint

Remember that disp shows the value of the variable, not the expression.

The code adds x and y (5 + 3) and stores in z, then displays z, which is 8.

🧠 Conceptual

intermediate

Understanding MATLAB script execution

Which statement best describes what happens when you run a MATLAB script file?

A MATLAB executes commands line by line in the script from top to bottom.

B MATLAB compiles the script into a standalone program before running.

C MATLAB runs all commands in the script simultaneously.

D MATLAB only checks the script for syntax errors but does not run it.

💡 Hint

Think about how you read a recipe or instructions.

MATLAB runs scripts line by line in order, executing each command sequentially.

🔧 Debug

advanced

Identify the error in this MATLAB code

What error will this MATLAB code produce when run?

MATLAB

a = 10
b = 20;
c = a + b;
disp(c);

A No error, output is 30

B Syntax error: Missing semicolon after first line

C Runtime error: Undefined variable 'a'

D Syntax error: Missing end statement

💡 Hint

In MATLAB, semicolons suppress output but are not required for correctness.

MATLAB allows lines without semicolons; it will display the value of 'a' but no error occurs.

❓ Predict Output

advanced

Output of a MATLAB script with string and numeric variables

What will be displayed when this MATLAB code runs?

MATLAB

name = 'Alice';
age = 25;
message = [name, ' is ', num2str(age), ' years old.'];
disp(message);

A Alice is age years old.

B Error: Cannot concatenate string and number directly.

C Alice is 25 years old.

D Alice is 25 years old

💡 Hint

num2str converts numbers to strings for concatenation.

The code converts age to string and concatenates with name and other text, then displays the full message.

🚀 Application

expert

Number of elements in a MATLAB array after operations

Consider this MATLAB code. How many elements does the variable 'result' contain after execution?

MATLAB

arr = 1:10;
result = arr(arr > 5);

A 6

B Error: Logical indexing not allowed

C 10

D 5

💡 Hint

Think about which numbers in arr are greater than 5.

arr > 5 is true for elements 6,7,8,9,10, so result contains 5 elements.

Practice

1. What does the MATLAB command disp('Hello, world!') do?

easy

A. It saves the text Hello, world! to a file.

B. It displays the text Hello, world! on the screen.

C. It creates a variable named Hello, world!.

D. It runs a loop that prints Hello, world! multiple times.

Solution

1. Step 1: Understand the disp function

   The disp function in MATLAB shows text or values on the screen.

2. Step 2: Analyze the input to disp

   The input is a string 'Hello, world!' which means it will print this exact text.

3. Final Answer:

   It displays the text Hello, world! on the screen. -> Option B

4. Quick Check:

   disp('text') shows text [OK]

Hint: disp shows text inside single quotes [OK]

Common Mistakes:

• Thinking disp saves text to a file
• Using double quotes instead of single quotes
• Confusing disp with variable creation

2. Which of the following is the correct syntax to display the message Hello in MATLAB?

easy

A. disp('Hello')

B. display(Hello)

C. disp(Hello)

D. print('Hello')

Solution

1. Step 1: Check the correct function name

   MATLAB uses disp to display messages, not display or print.

2. Step 2: Check the string syntax

   Strings must be inside single quotes in MATLAB, so disp('Hello') is correct.

3. Final Answer:

   disp('Hello') -> Option A

4. Quick Check:

   disp with single quotes is correct [OK]

Hint: Use disp with single quotes for text [OK]

Common Mistakes:

• Using double quotes instead of single quotes
• Using wrong function names like print or display
• Missing quotes around text

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

disp('Welcome to MATLAB!')

medium

A. Welcome to MATLAB!

B. disp('Welcome to MATLAB!')

C. SyntaxError

D. No output

Solution

1. Step 1: Understand disp function behavior

   The disp function prints the string inside the parentheses to the screen.

2. Step 2: Check the string format

   The string is correctly enclosed in single quotes, so it will print exactly as given.

3. Final Answer:

   Welcome to MATLAB! -> Option A

4. Quick Check:

   disp prints string text [OK]

Hint: disp prints text inside single quotes exactly [OK]

Common Mistakes:

• Expecting disp to print the command itself
• Using double quotes causing errors
• Forgetting to use disp function

4. Identify the error in this MATLAB code:

disp(Welcome to MATLAB!)

medium

A. Parentheses are not allowed with disp

B. Missing semicolon at the end

C. disp function does not exist

D. Text is not inside single quotes

Solution

1. Step 1: Check the input to disp

   The text Welcome to MATLAB! is not inside single quotes, so MATLAB treats it as variables or commands.

2. Step 2: Understand string syntax in MATLAB

   Strings must be enclosed in single quotes to be recognized as text.

3. Final Answer:

   Text is not inside single quotes -> Option D

4. Quick Check:

   Strings need single quotes [OK]

Hint: Always put text inside single quotes in disp [OK]

Common Mistakes:

• Omitting quotes around text
• Thinking semicolon is required for disp
• Believing disp is not a function

5. You want to write a MATLAB program that displays two lines:
Hello
and
Welcome to MATLAB
Which code will do this correctly?

hard

A. disp('Hello\nWelcome to MATLAB')

B. disp('Hello')
disp(Welcome to MATLAB)

C. disp('Hello')
disp('Welcome to MATLAB')

D. disp('Hello' + 'Welcome to MATLAB')

Solution

1. Step 1: Check how to display multiple lines

   Using two separate disp calls prints each line separately.

2. Step 2: Analyze each option

   disp('Hello') disp('Welcome to MATLAB') uses two disp calls with correct strings. disp('Hello\nWelcome to MATLAB') tries to use \n inside single quotes which MATLAB does not interpret as newline. disp('Hello') disp(Welcome to MATLAB) misses quotes in second disp. disp('Hello' + 'Welcome to MATLAB') tries to add strings which is invalid in MATLAB.

3. Final Answer:

   disp('Hello') disp('Welcome to MATLAB') -> Option C

4. Quick Check:

   Use separate disp calls for multiple lines [OK]

Hint: Use separate disp lines for multiple messages [OK]

Common Mistakes:

• Using \n inside single quotes expecting newline
• Missing quotes around text
• Trying to add strings with + operator