Script files and editor in MATLAB - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a simple script file

What is the output when you run this MATLAB script file named example.m?

MATLAB

a = 5;
b = 3;
c = a + b;
disp(c);

A 8

B 53

C a + b

D Error: Undefined function or variable 'c'.

💡 Hint

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

The script adds 5 and 3, stores in c, then displays c, which is 8.

❓ Predict Output

intermediate

Variable scope in script files

Given this script myscript.m:

a = 10;
b = 20;
c = a + b;

What will be the value of c in the MATLAB command window after running myscript?

MATLAB

a = 10;
b = 20;
c = a + b;

A 0

B 30

C Error: Variable 'c' is undefined.

D 30 but only inside the script, not in the command window.

💡 Hint

Script files share the workspace with the command window.

Variables created in scripts appear in the base workspace and can be accessed after running the script.

🔧 Debug

advanced

Identify the error in this script

What error will MATLAB show when running this script file named test.m?

MATLAB

x = 5
if x > 3
    disp('x is greater than 3');
end

A No error, output: x is greater than 3

B Syntax error: Missing semicolon after first line

C Syntax error: Missing 'end' for if statement

D Runtime error: Undefined variable 'x'

💡 Hint

In MATLAB, semicolons are optional to end statements.

MATLAB allows statements without semicolons; the if block is correctly closed with 'end'.

❓ Predict Output

advanced

Effect of clearing variables in script

Consider this script clear_test.m:

clear
x = 7;
y = x * 2;
disp(y);

What will be the output when you run clear_test?

MATLAB

clear
x = 7;
y = x * 2;
disp(y);

A 0

B Error: Undefined variable 'x'.

C 14

D No output, script clears all variables and stops.

💡 Hint

The clear command removes variables before new ones are created.

The script clears variables, then assigns x=7, y=14, and displays 14.

🧠 Conceptual

expert

Script file behavior with function definitions

What happens if you define a function inside a MATLAB script file and then call it within the same script?

MATLAB

disp(myfunc(3));

function y = myfunc(x)
    y = x^2;
end

A Error: Functions cannot be defined inside script files

B The script runs but outputs nothing

C Error: Function 'myfunc' is undefined when called

D The script runs and outputs 9

💡 Hint

Since MATLAB R2016b, local functions can be included in scripts.

Modern MATLAB allows local functions in scripts; calling them works and outputs 9.

Practice

1. What is the main purpose of a script file in MATLAB?

easy

A. To create graphical user interfaces

B. To save and run a group of commands together

C. To store variables permanently

D. To compile MATLAB code into an executable

Solution

1. Step 1: Understand what script files do

   Script files contain a sequence of MATLAB commands saved in a file to run together.

2. Step 2: Compare options with script file purpose

   Only To save and run a group of commands together describes saving and running commands together, which is the main use of scripts.

3. Final Answer:

   To save and run a group of commands together -> Option B

4. Quick Check:

   Script files = save and run commands [OK]

Hint: Scripts group commands to run all at once [OK]

Common Mistakes:

• Confusing scripts with functions
• Thinking scripts store variables permanently
• Assuming scripts compile code

2. Which of the following is the correct way to save a script file in MATLAB Editor?

easy

A. Click File > Save or press Ctrl+S

B. Type save script in the command window

C. Right-click the command window and select Save

D. Use the command saveas('filename') in the script

Solution

1. Step 1: Identify how to save files in MATLAB Editor

   The Editor uses standard save options like File menu or Ctrl+S shortcut.

2. Step 2: Evaluate each option

   Only Click File > Save or press Ctrl+S correctly describes saving via Editor menu or shortcut. Others are incorrect or commands for different purposes.

3. Final Answer:

   Click File > Save or press Ctrl+S -> Option A

4. Quick Check:

   Save script = File menu or Ctrl+S [OK]

Hint: Use File menu or Ctrl+S to save scripts [OK]

Common Mistakes:

• Trying to save scripts from command window
• Using saveas command incorrectly
• Right-clicking command window instead of Editor

3. What will be the output when running this script in MATLAB Editor?

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

medium

A. 8

B. 53

C. x + y

D. Error: Undefined variable

Solution

1. Step 1: Understand the script commands

   Variables x and y are assigned 5 and 3, then z is sum of x and y.

2. Step 2: Calculate the value of z and output

   z = 5 + 3 = 8, disp(z) prints 8 to the command window.

3. Final Answer:

   8 -> Option A

4. Quick Check:

   5 + 3 = 8 output [OK]

Hint: Add variables then display result [OK]

Common Mistakes:

• Concatenating numbers as strings
• Expecting variable names printed
• Assuming error without variable initialization

4. Identify the error in this MATLAB script:

for i = 1:3
  disp(i)
endd

medium

A. disp function used incorrectly

B. Missing semicolon after disp(i)

C. Loop variable i is not defined

D. Incorrect end keyword spelling

Solution

1. Step 1: Check the loop syntax

   The for loop uses 'endd' instead of 'end' to close the loop.

2. Step 2: Identify the syntax error

   MATLAB requires 'end' keyword exactly; 'endd' causes a syntax error.

3. Final Answer:

   Incorrect end keyword spelling -> Option D

4. Quick Check:

   Loop ends with 'end' keyword [OK]

Hint: Use exact 'end' to close loops [OK]

Common Mistakes:

• Typing 'endd' instead of 'end'
• Forgetting to close loops
• Adding unnecessary semicolons

5. You want to create a script that calculates the average of numbers stored in a vector data. Which script structure correctly computes and displays the average?

hard

A. avg = mean(data)
disp(total);

B. for i = 1:length(data)
avg = data(i) / length(data);
end
disp(avg);

C. total = sum(data);
count = length(data);
avg = total / count;
disp(avg);

D. avg = sum(data) * length(data);
disp(avg);

Solution

1. Step 1: Understand how to calculate average

   Average = sum of elements divided by number of elements.

2. Step 2: Check each script option

   total = sum(data);
   count = length(data);
   avg = total / count;
   disp(avg);

   correctly sums data, counts elements, divides, then displays average. Others have errors: A displays undefined total, C overwrites avg incorrectly in loop, D multiplies instead of dividing.

3. Final Answer:

   total = sum(data); count = length(data); avg = total / count; disp(avg); -> Option C

4. Quick Check:

   Average = sum / count [OK]

Hint: Average = sum divided by count, then display [OK]

Common Mistakes:

• Using mean without displaying correct variable
• Calculating average inside loop incorrectly
• Multiplying sum by length instead of dividing