While loops in MATLAB - Mini Project: Build & Apply

Using While Loops in MATLAB

📖 Scenario: You are helping a cashier count the total number of coins collected in a jar. The jar contains coins of different values, but you only want to count coins until the total value reaches or exceeds a certain amount.

🎯 Goal: Build a MATLAB program that uses a while loop to add coin values one by one until the total reaches a target amount.

📋 What You'll Learn

Create a vector called coins with the exact values: [1, 5, 10, 25, 1, 10]

Create a variable called target and set it to 30

Use a while loop to add coin values from coins until the total is at least target

Print the final total value after the loop ends

💡 Why This Matters

🌍 Real World

Counting coins or items until a certain limit is reached is common in cash handling, inventory, and budgeting tasks.

💼 Career

Understanding while loops helps automate repetitive tasks and control program flow in many engineering and data processing jobs.

1

Create the coin values vector

Create a vector called coins with these exact values: [1, 5, 10, 25, 1, 10]

MATLAB

% Create the coins vector
% Your code here

Hint

Use square brackets [] to create a vector with the given numbers separated by commas.

2

Set the target total value

Create a variable called target and set it to 30

MATLAB

coins = [1, 5, 10, 25, 1, 10];
% Create the target variable
% Your code here

Hint

Use the assignment operator = to set target to 30.

3

Use a while loop to sum coin values

Create variables total set to 0 and index set to 1. Then use a while loop with the condition total < target && index <= length(coins) to add coins(index) to total and increase index by 1 inside the loop.

MATLAB

coins = [1, 5, 10, 25, 1, 10];
target = 30;
% Initialize total and index
% Your code here

% Use a while loop to add coins until total reaches target
% Your code here

Hint

Remember to initialize total and index before the loop. Use while with the condition that total is less than target and index is within the vector length.

4

Display the final total value

Use disp to print the value of total after the loop ends.

MATLAB

coins = [1, 5, 10, 25, 1, 10];
target = 30;
total = 0;
index = 1;
while total < target && index <= length(coins)
    total = total + coins(index);
    index = index + 1;
end
% Display the total
% Your code here

Hint

Use disp(total) to show the final total value on the screen.

Practice

1. What does a while loop do in MATLAB?

easy

A. Repeats a block of code as long as a condition is true

B. Executes code only once

C. Runs code a fixed number of times

D. Stops the program immediately

Solution

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

   A while loop runs repeatedly while its condition remains true.

2. Step 2: Compare options with definition

   Only Repeats a block of code as long as a condition is true correctly describes this behavior.

3. Final Answer:

   Repeats a block of code as long as a condition is true -> Option A

4. Quick Check:

   While loop = repeat while true [OK]

Hint: While loops run while condition is true, not fixed times [OK]

Common Mistakes:

• Thinking while loops run a fixed number of times
• Confusing while with if statement
• Believing while loops run only once

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

easy

A. while condition
statements
end

B. while (condition) {
statements
}

C. while condition:
statements
end

D. while condition do
statements
end

Solution

1. Step 1: Recall MATLAB while loop syntax

   MATLAB uses 'while condition' followed by statements and ends with 'end'.

2. Step 2: Check each option

   while condition statements end matches MATLAB syntax; others use syntax from other languages.

3. Final Answer:

   while condition\n statements\nend -> Option A

4. Quick Check:

   MATLAB uses 'end' to close loops [OK]

Hint: MATLAB while loops end with 'end', no braces [OK]

Common Mistakes:

• Using braces {} instead of 'end'
• Adding colons after condition
• Using 'do' keyword

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

i = 1;
while i <= 3
  disp(i)
  i = i + 1;
end

medium

A. 1 2 3 4

B. 1 2 3

C. 1 2

D. Error: infinite loop

Solution

1. Step 1: Analyze loop condition and increments

   The loop runs while i is less than or equal to 3, starting at 1 and increasing by 1 each time.

2. Step 2: Trace output values

   Values displayed are 1, then 2, then 3. When i becomes 4, condition fails and loop stops.

3. Final Answer:

   1 2 3 -> Option B

4. Quick Check:

   Loop prints 1 to 3 [OK]

Hint: Increment loop variable to avoid infinite loop [OK]

Common Mistakes:

• Forgetting to increment i causing infinite loop
• Expecting output to include 4
• Confusing loop condition with < instead of <=

4. Identify the error in this MATLAB code snippet:

count = 5;
while count > 0
  disp(count)
end

medium

A. disp function cannot be used inside while

B. Incorrect while syntax

C. Missing increment or decrement inside the loop

D. Variable 'count' not initialized

Solution

1. Step 1: Check loop condition and body

   The loop condition is 'count > 0', but inside the loop count is never changed.

2. Step 2: Understand effect of missing update

   Without changing count, the condition stays true forever, causing an infinite loop.

3. Final Answer:

   Missing increment or decrement inside the loop -> Option C

4. Quick Check:

   Update loop variable to avoid infinite loop [OK]

Hint: Always update loop variable inside while loop [OK]

Common Mistakes:

• Forgetting to change loop variable
• Assuming disp causes error
• Thinking syntax is wrong

5. Write a MATLAB while loop that sums numbers from 1 to 10 and stores the result in total. Which code correctly does this?

hard

A. total = 0;
i = 1;
while i <= 10
total = total + i;
i = i - 1;
end

B. total = 0;
i = 1;
while i < 10
total = total + i;
end

C. total = 0;
for i = 1:10
total = total + i;
end

D. total = 0;
i = 1;
while i <= 10
total = total + i;
i = i + 1;
end

Solution

1. Step 1: Understand the goal and loop condition

   We want to add numbers 1 through 10 using a while loop that stops when i > 10.

2. Step 2: Check each option for correctness

   total = 0; i = 1; while i <= 10 total = total + i; i = i + 1; end initializes total and i, adds i to total, increments i, and stops at 10 correctly. total = 0; i = 1; while i < 10 total = total + i; end misses increment causing infinite loop. total = 0; for i = 1:10 total = total + i; end uses for loop, not while. total = 0; i = 1; while i <= 10 total = total + i; i = i - 1; end decrements i causing infinite loop.

3. Final Answer:

   total = 0;\ni = 1;\nwhile i <= 10\n total = total + i;\n i = i + 1;\nend -> Option D

4. Quick Check:

   Increment i to sum 1 to 10 [OK]

Hint: Increment loop variable to reach end condition [OK]

Common Mistakes:

• Forgetting to increment i
• Using for loop instead of while
• Decrementing i causing infinite loop