For loops in MATLAB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a for loop that counts from 1 to 5.

MATLAB

for i = [1]
    disp(i)
end

Drag options to blanks, or click blank then click option'

A1 to 5

B1,5

C1:5

D[1 5]

Attempts:

3 left

💡 Hint

Common Mistakes

Using commas instead of colon to create the range.

Using square brackets which create a vector but not a range for the loop.

The syntax 1:5 creates a range from 1 to 5 in MATLAB, which is used in the for loop.

2fill in blank

medium

Complete the code to sum numbers from 1 to 10 using a for loop.

MATLAB

total = 0;
for n = 1:10
    total = total + [1];
end

Drag options to blanks, or click blank then click option'

A10

Btotal

C1

Dn

Attempts:

3 left

💡 Hint

Common Mistakes

Adding the total to itself instead of the loop variable.

Adding a fixed number like 10 or 1 instead of the loop variable.

Inside the loop, n is the current number from 1 to 10, so we add it to total.

3fill in blank

hard

Fix the error in the for loop to display numbers from 5 down to 1.

MATLAB

for i = [1]
    disp(i)
end

Drag options to blanks, or click blank then click option'

A1:5

B5:-1:1

C5:1

D1:-1:5

Attempts:

3 left

💡 Hint

Common Mistakes

Using 5:1 which counts up and results in an empty loop.

Using 1:-1:5 which is an invalid range.

To count down from 5 to 1, use the syntax 5:-1:1 which means start at 5, step by -1, end at 1.

4fill in blank

hard

Fill both blanks to create a for loop that prints only even numbers from 2 to 10.

MATLAB

for i = [1]:[2]:10
    disp(i)
end

Drag options to blanks, or click blank then click option'

A2

B1

D3

Attempts:

3 left

💡 Hint

Common Mistakes

Using 1 as the start or step which prints odd numbers.

Using 3 as the step which skips some even numbers.

The loop starts at 2 and steps by 2 to print even numbers up to 10.

5fill in blank

hard

Fill all three blanks to create a for loop that prints the squares of numbers from 1 to 5.

MATLAB

for [1] = [2]:[3]:5
    disp([1]^2)
end

Drag options to blanks, or click blank then click option'

Ai

B1

D2

Attempts:

3 left

💡 Hint

Common Mistakes

Using a step other than 1 which skips numbers.

Using a variable name other than i which is conventional here.

The loop variable i goes from 1 to 5 in steps of 1, and we display its square.

Practice

1. What does a for loop do in MATLAB?

easy

A. Stops the program immediately

B. Runs commands only once

C. Creates a new variable

D. Repeats a set of commands a fixed number of times

Solution

1. Step 1: Understand the purpose of a for loop

   A for loop is designed to repeat commands multiple times based on a range or list.

2. Step 2: Compare options with the definition

   Only Repeats a set of commands a fixed number of times correctly describes repeating commands a fixed number of times.

3. Final Answer:

   Repeats a set of commands a fixed number of times -> Option D

4. Quick Check:

   For loop = repeat commands [OK]

Hint: For loops repeat commands multiple times [OK]

Common Mistakes:

• Thinking for loops run only once
• Confusing for loops with if statements
• Believing for loops stop the program

2. Which of the following is the correct syntax for a for loop in MATLAB?

easy

A. for i = 1:5
disp(i)
end

B. for (i = 1; i <= 5; i++)
disp(i)
end

C. loop i from 1 to 5
disp(i)
end

D. for i in range(1,5):
disp(i)

Solution

1. Step 1: Identify MATLAB for loop syntax

   MATLAB uses 'for variable = start:end' and ends with 'end'.

2. Step 2: Check each option

   for i = 1:5 disp(i) end matches MATLAB syntax. Options B, C, and D use other languages' syntax.

3. Final Answer:

   for i = 1:5\n disp(i)\nend -> Option A

4. Quick Check:

   MATLAB for loop = for i = 1:5 ... end [OK]

Hint: MATLAB for loops use 'for var = start:end' and end with 'end' [OK]

Common Mistakes:

• Using parentheses like C or JavaScript
• Using Python or other language syntax
• Forgetting the 'end' keyword

3. What is the output of this MATLAB code?

sum = 0;
for i = 1:3
  sum = sum + i;
end
disp(sum)

medium

A. 6

B. 3

C. 0

D. Error

Solution

1. Step 1: Trace the loop iterations

   The loop runs i = 1, 2, 3. sum starts at 0.

2. Step 2: Calculate sum after each iteration

   sum = 0+1=1, then 1+2=3, then 3+3=6.

3. Final Answer:

   6 -> Option A

4. Quick Check:

   1+2+3 = 6 [OK]

Hint: Add numbers 1 to 3 inside loop [OK]

Common Mistakes:

• Forgetting to initialize sum
• Adding outside the loop
• Confusing loop range

4. Identify the error in this MATLAB for loop:

for i = 1:4
  disp(i)
  i = i + 1;
end

medium

A. Missing 'end' keyword

B. Modifying loop variable inside the loop

C. Incorrect loop range syntax

D. disp function is invalid

Solution

1. Step 1: Review loop variable usage

   The loop variable 'i' is controlled by MATLAB and should not be changed inside the loop.

2. Step 2: Identify the problem

   Changing 'i' inside the loop causes unexpected behavior or errors.

3. Final Answer:

   Modifying loop variable inside the loop -> Option B

4. Quick Check:

   Do not change loop variable inside for loop [OK]

Hint: Never change the loop variable inside the loop [OK]

Common Mistakes:

• Changing loop variable inside loop body
• Forgetting 'end' keyword (not the case here)
• Misunderstanding disp function

5. How can you use a for loop in MATLAB to create a vector v containing squares of numbers from 1 to 5?

hard

A. v = [];
for i = 1:5
v = v + i^2;
end

B. for i = 1:5
v(i) = i*2;
end

C. v = zeros(1,5);
for i = 1:5
v(i) = i^2;
end

D. v = 1:5;
for i = 1:5
v(i) = i + 2;
end

Solution

1. Step 1: Initialize vector to store results

   Pre-allocate vector v with zeros to hold 5 elements.

2. Step 2: Use for loop to assign squares

   For each i from 1 to 5, assign v(i) = i squared.

3. Final Answer:

   v = zeros(1,5);\nfor i = 1:5\n v(i) = i^2;\nend -> Option C

4. Quick Check:

   Pre-allocate vector and assign squares in loop [OK]

Hint: Pre-allocate vector, assign squares inside loop [OK]

Common Mistakes:

• Not pre-allocating vector before loop
• Adding instead of assigning inside loop
• Using wrong operation for squares