For loops in MATLAB - Mini Project: Build & Apply

For loops

📖 Scenario: You work in a small store and want to calculate the total price of items bought by a customer. Each item has a price, and you want to add them all up.

🎯 Goal: Build a MATLAB program that uses a for loop to add up the prices of items in a list and print the total cost.

📋 What You'll Learn

Create a vector called prices with the exact values: 10, 20, 15, 5, 30

Create a variable called total and set it to 0

Use a for loop with the variable i to iterate over the elements of prices

Add each price to total inside the loop

Print the final value of total using disp

💡 Why This Matters

🌍 Real World

Calculating totals is common in stores, restaurants, and anywhere money is counted.

💼 Career

Understanding loops and summing values is a basic skill for data analysis, finance, and programming jobs.

1

Create the prices vector

Create a vector called prices with these exact values: 10, 20, 15, 5, 30

MATLAB

% Create the prices vector with the given values
% Your code here

Hint

Use square brackets [] to create a vector in MATLAB.

2

Initialize the total variable

Create a variable called total and set it to 0

MATLAB

prices = [10, 20, 15, 5, 30];
% Create a variable total and set it to 0
% Your code here

Hint

Use = to assign the value 0 to the variable total.

3

Use a for loop to sum prices

Use a for loop with the variable i to iterate over the elements of prices. Inside the loop, add prices(i) to total

MATLAB

prices = [10, 20, 15, 5, 30];
total = 0;
% Use a for loop to add each price to total
% Your code here

Hint

Use length(prices) to get the number of elements in the vector.

4

Display the total price

Use disp(total) to print the final value of total

MATLAB

prices = [10, 20, 15, 5, 30];
total = 0;
for i = 1:length(prices)
    total = total + prices(i);
end
% Display the total price
% Your code here

Hint

Use disp to show the value stored in total.

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