Properties and methods in MATLAB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a property named age in the class.

MATLAB

classdef Person
    properties
        [1]
    end
end

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

Aclass

Bfunction

Cmethods

Dage

Attempts:

3 left

💡 Hint

Common Mistakes

Writing function or methods inside the properties block.

Forgetting to put the property name inside the properties block.

The properties block defines variables for the class. Here, age is a property.

2fill in blank

medium

Complete the code to define a method named greet inside the class.

MATLAB

classdef Person
    methods
        function [1](obj)
            disp('Hello!')
        end
    end
end

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

Aage

BPerson

Cgreet

Dhello

Attempts:

3 left

💡 Hint

Common Mistakes

Using a property name instead of a method name.

Using the class name as the method name.

The method name follows the function keyword. Here, greet is the method name.

3fill in blank

hard

Fix the error in the method definition by completing the code.

MATLAB

classdef Person
    properties
        name
    end
    methods
        function obj = [1](newName)
            obj.name = newName;
        end
    end
end

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

Agreet

BPerson

CsetName

Dname

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different method name than the class name for the constructor.

Using a property name as the constructor method name.

The constructor method must have the same name as the class, which is Person.

4fill in blank

hard

Fill both blanks to create a method that returns the name property.

MATLAB

classdef Person
    properties
        name
    end
    methods
        function [1] = getName(obj)
            [2] = obj.name;
        end
    end
end

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

Aoutput

Bresult

Cname

Dobj

Attempts:

3 left

💡 Hint

Common Mistakes

Using the property name as the output variable.

Using the object variable obj as the output.

The method output variable is declared after the function keyword, and the output is assigned inside the method.

5fill in blank

hard

Fill all three blanks to define a method that sets the age property.

MATLAB

classdef Person
    properties
        age
    end
    methods
        function obj = [1](obj, [2])
            obj.[3] = [2];
        end
    end
end

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

AsetAge

BnewAge

Cage

Dobj

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong method name.

Confusing the input argument with the property name.

The method name is setAge, the input argument is newAge, and the property age is set to this input.

Practice

1. In MATLAB, what is the main purpose of properties in a class definition?

easy

A. To define functions that perform actions

B. To create loops inside the class

C. To store data related to the object

D. To handle errors during execution

Solution

1. Step 1: Understand what properties represent

   Properties in MATLAB classes are used to hold data or attributes about the object.

2. Step 2: Differentiate properties from methods

   Methods are functions that act on the data, not the data itself.

3. Final Answer:

   To store data related to the object -> Option C

4. Quick Check:

   Properties = Data storage [OK]

Hint: Properties always hold data, methods perform actions [OK]

Common Mistakes:

• Confusing properties with methods
• Thinking properties are for functions
• Assuming properties handle errors

2. Which of the following is the correct way to define a method inside a MATLAB class?

easy

A. methods
function obj = setValue(obj, val)
obj.Value = val;
end
end

B. properties
function obj = setValue(obj, val)
obj.Value = val;
end
end

C. function setValue(obj, val)
obj.Value = val;
end

D. methods
obj.Value = val;
end

Solution

1. Step 1: Identify method block syntax

   Methods in MATLAB classes are defined inside a methods block.

2. Step 2: Check function definition inside methods

   The function must have the object as input and output if modifying properties.

3. Final Answer:

   methods function obj = setValue(obj, val) obj.Value = val; end end -> Option A

4. Quick Check:

   Methods block + function syntax = methods function obj = setValue(obj, val) obj.Value = val; end end [OK]

Hint: Methods go inside 'methods' block with function keyword [OK]

Common Mistakes:

• Placing functions inside properties block
• Omitting the methods keyword
• Not returning the modified object

3. Consider the following MATLAB class snippet:

classdef MyClass
  properties
    Value
  end
  methods
    function obj = setValue(obj, val)
      obj.Value = val;
    end
    function v = getValue(obj)
      v = obj.Value;
    end
  end
end

obj = MyClass();
obj = obj.setValue(10);
disp(obj.getValue());

What will be the output when this code runs?

medium

A. 0

B. obj.Value

C. Error: Undefined function or variable 'Value'

D. 10

Solution

1. Step 1: Understand method calls and property assignment

   The method setValue sets the property Value to 10 and returns the updated object.

2. Step 2: Check the output of getValue

   The getValue method returns the current value of the property Value, which is 10.

3. Final Answer:

   10 -> Option D

4. Quick Check:

   Property set and get returns 10 [OK]

Hint: Methods update and return object; get method returns stored value [OK]

Common Mistakes:

• Forgetting to assign returned object from setValue
• Expecting property access without method
• Confusing property name with variable

4. Identify the error in this MATLAB class method definition:

methods
  function setValue(obj, val)
    obj.Value = val;
  end
end

medium

A. The method must return the modified object

B. The method name is invalid

C. Properties block is missing

D. The function keyword is not allowed inside methods

Solution

1. Step 1: Check method signature for modifying properties

   In MATLAB, when a method modifies object properties, it must return the updated object.

2. Step 2: Identify missing return value

   The method setValue does not return obj, so changes won't persist.

3. Final Answer:

   The method must return the modified object -> Option A

4. Quick Check:

   Modify method must return object [OK]

Hint: Return updated object when changing properties [OK]

Common Mistakes:

• Not returning the object after modification
• Assuming properties change without return
• Confusing function keyword usage

5. You want to create a MATLAB class BankAccount with a property Balance and a method deposit that adds money to the balance only if the amount is positive. Which of the following method definitions correctly implements this?

hard

A. methods
function deposit(obj, amount)
if amount > 0
obj.Balance = obj.Balance + amount;
end
end
end

B. methods
function obj = deposit(obj, amount)
if amount > 0
obj.Balance = obj.Balance + amount;
end
end
end

C. methods
function obj = deposit(amount)
if amount > 0
obj.Balance = obj.Balance + amount;
end
end
end

D. methods
function obj = deposit(obj, amount)
obj.Balance = obj.Balance + amount;
end
end

Solution

1. Step 1: Check method signature for modifying object

   The method must accept the object and amount, and return the updated object.

2. Step 2: Verify condition for positive amount

   The method correctly adds amount only if it is greater than zero.

3. Step 3: Identify incorrect options

   methods function deposit(obj, amount) if amount > 0 obj.Balance = obj.Balance + amount; end end end does not return the object, so changes won't persist. methods function obj = deposit(amount) if amount > 0 obj.Balance = obj.Balance + amount; end end end misses the object input. methods function obj = deposit(obj, amount) obj.Balance = obj.Balance + amount; end end adds amount without checking if positive.

4. Final Answer:

   methods function obj = deposit(obj, amount) if amount > 0 obj.Balance = obj.Balance + amount; end end end -> Option B

5. Quick Check:

   Return updated object and check amount > 0 [OK]

Hint: Return object and check positive amount before adding [OK]

Common Mistakes:

• Not returning updated object
• Missing object input argument
• Not checking if amount is positive