Class definition syntax in MATLAB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a simple class named MyClass.

MATLAB

classdef [1]
end

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

AMyClass

Bfunction

Cscript

Dmethod

Attempts:

3 left

💡 Hint

Common Mistakes

Using keywords like function or script instead of the class name.

Leaving the class name blank.

The keyword classdef is followed by the class name, here MyClass.

2fill in blank

medium

Complete the code to add a property named 'Value' to the class.

MATLAB

classdef Sample
    properties
        [1]
    end
end

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

Afunction

Bend

Cmethods

DValue

Attempts:

3 left

💡 Hint

Common Mistakes

Writing 'function' or 'methods' inside properties block.

Forgetting to name the property.

Inside the properties block, list property names like Value.

3fill in blank

hard

Fix the error in the method definition by completing the function header.

MATLAB

classdef Calc
    methods
        function result = [1](obj, x, y)
            result = x + y;
        end
    end
end

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

Aadd

BCalc

Cproperties

Dmethods

Attempts:

3 left

💡 Hint

Common Mistakes

Using the class name as the method name.

Using keywords like 'properties' or 'methods' as method names.

The method name follows the function keyword; here it is add.

4fill in blank

hard

Fill both blanks to define a class with a property and a method that returns that property.

MATLAB

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

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

AName

BPerson

CgetName

DValue

Attempts:

3 left

💡 Hint

Common Mistakes

Mismatching property and method names.

Using class name as method name.

The property is named Name and the method to get it is getName.

5fill in blank

hard

Fill all three blanks to define a class with a property, a constructor, and a method that returns the property.

MATLAB

classdef Car
    properties
        [1]
    end
    methods
        function obj = [2](inputColor)
            obj.Color = inputColor;
        end
        function c = [3](obj)
            c = obj.Color;
        end
    end
end

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

AColor

BCar

CgetColor

DValue

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong names for constructor or method.

Mismatching property and method names.

The property is Color, the constructor is named after the class Car, and the method to get the color is getColor.

Practice

1. Which keyword is used to start a class definition in MATLAB?

easy

A. class

B. classdef

C. defineclass

D. objectdef

Solution

1. Step 1: Recall MATLAB class syntax

   In MATLAB, classes always start with the keyword classdef.

2. Step 2: Compare options

   Only classdef uses classdef, the correct keyword for defining classes.

3. Final Answer:

   classdef -> Option B

4. Quick Check:

   Class start keyword = classdef [OK]

Hint: Remember: MATLAB classes start with 'classdef' keyword [OK]

Common Mistakes:

• Using 'class' instead of 'classdef'
• Confusing with other languages' syntax
• Forgetting to use any keyword

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

easy

A. attributes
x
end

B. property
x
end

C. properties
x
end

D. props
x
end

Solution

1. Step 1: Recall properties block syntax

   In MATLAB, class data members are defined inside a properties block.

2. Step 2: Check each option

   Only properties x end uses the correct keyword properties to define data.

3. Final Answer:

   properties block -> Option C

4. Quick Check:

   Data inside 'properties' block [OK]

Hint: Use 'properties' keyword to define class data [OK]

Common Mistakes:

• Using 'property' instead of 'properties'
• Using 'props' or 'attributes' which are invalid
• Placing properties outside the classdef block

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

classdef MyClass
    properties
        Value = 10;
    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(25);
disp(obj.getValue());

medium

A. 25

B. 10

C. Error: Cannot assign value

D. 0

Solution

1. Step 1: Understand property initialization

   The property Value starts at 10.

2. Step 2: Follow method calls

   The method setValue sets Value to 25, then getValue returns it.

3. Final Answer:

   25 -> Option A

4. Quick Check:

   Value updated to 25 and displayed [OK]

Hint: Setter updates property; getter returns updated value [OK]

Common Mistakes:

• Forgetting to assign returned object from setter
• Expecting initial value instead of updated
• Assuming direct property change without methods

4. Identify the error in this MATLAB class definition:

classdef Sample
    properties
        Data
    end
    methods
        function obj = Sample(val)
            Data = val;
        end
    end
end

medium

A. Missing semicolon after Data property

B. Incorrect classdef keyword usage

C. Properties block should be inside methods

D. Constructor does not assign value to object property

Solution

1. Step 1: Check constructor assignment

   The constructor assigns val to Data without obj., so it does not update the object property.

2. Step 2: Understand correct assignment

   It should be obj.Data = val; to update the property.

3. Final Answer:

   Constructor does not assign value to object property -> Option D

4. Quick Check:

   Use 'obj.Data = val;' in constructor [OK]

Hint: Use 'obj.Property = value;' inside methods [OK]

Common Mistakes:

• Assigning property without 'obj.' prefix
• Placing properties inside methods block
• Missing constructor function name matching class

5. How can you define a MATLAB class with a property Count that starts at 0 and a method increment that adds 1 to Count each time it is called? Choose the correct complete class definition.

hard

A. classdef Counter
properties
Count = 0;
end
methods
function obj = increment(obj)
obj.Count = obj.Count + 1;
end
end
end

B. classdef Counter
properties
Count;
end
methods
function increment(obj)
Count = Count + 1;
end
end
end

C. classdef Counter
properties
Count = 0;
end
methods
function increment(obj)
obj.Count = obj.Count + 1;
end
end
end

D. classdef Counter
properties
Count = 0;
end
methods
function obj = increment(obj)
Count = Count + 1;
end
end
end

Solution

1. Step 1: Initialize property correctly

   The property Count must start at 0, so initialize it as Count = 0;.

2. Step 2: Define method with object output and update property

   The method increment must accept and return the object (obj) and update obj.Count by adding 1.

3. Step 3: Check each option

   classdef Counter
       properties
           Count = 0;
       end
       methods
           function obj = increment(obj)
               obj.Count = obj.Count + 1;
           end
       end
   end

   correctly initializes Count, defines increment with obj input/output, and updates obj.Count. Others miss one or more of these.

4. Final Answer:

   Option A is the correct full class definition -> Option A

5. Quick Check:

   Property init + method with obj input/output =

   classdef Counter
       properties
           Count = 0;
       end
       methods
           function obj = increment(obj)
               obj.Count = obj.Count + 1;
           end
       end
   end

   [OK]

Hint: Methods changing properties must return updated object [OK]

Common Mistakes:

• Not returning updated object from method
• Updating property without 'obj.' prefix
• Not initializing property value