Structures and field access in MATLAB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a structure with a field named 'name'.

MATLAB

person.[1] = 'Alice';

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

Aweight

Bname

Cheight

Dage

Attempts:

3 left

💡 Hint

Common Mistakes

Using a field name that does not match the value, like 'age' or 'height'.

Forgetting to use the dot (.) to access the field.

The field 'name' is assigned the value 'Alice' in the structure 'person'.

2fill in blank

medium

Complete the code to access the 'age' field from the structure 'person'.

MATLAB

ageValue = person.[1];

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

Aheight

Bweight

Cname

Dage

Attempts:

3 left

💡 Hint

Common Mistakes

Using a wrong field name like 'height' or 'name'.

Missing the dot (.) before the field name.

Accessing the 'age' field of the structure 'person' stores its value in 'ageValue'.

3fill in blank

hard

Fix the error in the code to correctly assign the field 'score' in the structure 'student'.

MATLAB

student[1]score = 95;

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

A.

B:

C;

D,

Attempts:

3 left

💡 Hint

Common Mistakes

Using colon (:) or semicolon (;) instead of dot (.) for field access.

Forgetting the dot entirely.

In MATLAB, the dot (.) is used to access or assign fields in a structure.

4fill in blank

hard

Fill both blanks to create a structure 'car' with fields 'make' and 'year'.

MATLAB

car.[1] = 'Toyota';
car.[2] = 2020;

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

Amake

Bmodel

Cyear

Dcolor

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up field names like using 'model' or 'color' instead of 'make' or 'year'.

Forgetting to use the dot (.) before field names.

The structure 'car' has fields 'make' and 'year' assigned with 'Toyota' and 2020 respectively.

5fill in blank

hard

Fill all three blanks to create a structure 'book' with fields 'title', 'author', and 'pages'.

MATLAB

book.[1] = '1984';
book.[2] = 'Orwell';
book.[3] = 328;

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

Aauthor

Bpages

Ctitle

Dpublisher

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect field names like 'publisher' instead of 'author' or 'pages'.

Mixing the order of fields.

The structure 'book' has fields 'title', 'author', and 'pages' with appropriate values.

Practice

1. What is the correct way to access the field age from a structure person in MATLAB?

easy

A. person['age']

B. person.age

C. person->age

D. person.age()

Solution

1. Step 1: Understand MATLAB structure field access

   In MATLAB, fields of a structure are accessed using dot notation without parentheses or brackets.

2. Step 2: Identify correct syntax for field access

   The correct syntax is structure.field, so person.age is correct.

3. Final Answer:

   person.age -> Option B

4. Quick Check:

   Use dot notation for fields [OK]

Hint: Use dot notation to access structure fields in MATLAB [OK]

Common Mistakes:

• Using parentheses like a function call
• Using brackets like a dictionary
• Using arrow notation from other languages

2. Which of the following is the correct way to create a structure car with fields make and year in MATLAB?

easy

A. car = struct(make = 'Toyota', year = 2020);

B. car = {make: 'Toyota', year: 2020};

C. car = struct['make' => 'Toyota', 'year' => 2020];

D. car = struct('make', 'Toyota', 'year', 2020);

Solution

1. Step 1: Recall MATLAB struct creation syntax

   MATLAB uses the struct function with pairs of field names and values as strings and values.

2. Step 2: Match correct syntax

   car = struct('make', 'Toyota', 'year', 2020); uses struct('make', 'Toyota', 'year', 2020), which is correct MATLAB syntax.

3. Final Answer:

   car = struct('make', 'Toyota', 'year', 2020); -> Option D

4. Quick Check:

   Use struct('field', value, ...) to create structures [OK]

Hint: Use struct('field', value) pairs to create structures [OK]

Common Mistakes:

• Using JSON or dictionary syntax
• Using equal signs inside struct()
• Using brackets instead of parentheses

3. What is the output of the following MATLAB code?

person.name = 'Alice';
person.age = 30;
disp(person.age);

medium

A. 'Alice'

B. name

C. 30

D. Error: Undefined variable

Solution

1. Step 1: Understand structure field assignment

   The code assigns 'Alice' to person.name and 30 to person.age.

2. Step 2: Identify what disp(person.age) shows

   The disp function prints the value of person.age, which is 30.

3. Final Answer:

   30 -> Option C

4. Quick Check:

   disp shows the value of the accessed field [OK]

Hint: disp(struct.field) prints the field's value [OK]

Common Mistakes:

• Confusing field names with values
• Expecting the field name instead of value
• Syntax errors from missing semicolons

4. Consider this MATLAB code snippet:

data = struct('x', 10, 'y', 20);
disp(data.z);

What will happen when this code runs?

medium

A. Error: Reference to non-existent field 'z'.

B. Displays 0

C. Displays empty array []

D. Displays 20

Solution

1. Step 1: Check structure fields

   The structure data has fields x and y, but no field z.

2. Step 2: Accessing a non-existent field

   Trying to access data.z causes MATLAB to throw an error about the missing field.

3. Final Answer:

   Error: Reference to non-existent field 'z'. -> Option A

4. Quick Check:

   Accessing missing fields causes an error [OK]

Hint: Access only existing fields; missing fields cause errors [OK]

Common Mistakes:

• Assuming missing fields return 0 or empty
• Ignoring error messages
• Confusing field names with variable names

5. You have a structure array students with fields name and score. How do you create a new structure passed containing only students with score >= 50?

hard

A. passed = students([students.score] >= 50);

B. passed = struct('name', students.name, 'score', students.score >= 50);

C. passed = students.score >= 50;

D. passed = students{students.score >= 50};

Solution

1. Step 1: Understand structure arrays and logical indexing

   In MATLAB, [students.score] creates an array of scores. Logical indexing selects elements where condition is true.

2. Step 2: Apply logical indexing to filter students

   The expression students([students.score] >= 50) selects only students with scores 50 or above.

3. Final Answer:

   passed = students([students.score] >= 50); -> Option A

4. Quick Check:

   Use logical indexing on structure arrays [OK]

Hint: Use logical indexing with [struct.field] to filter arrays [OK]

Common Mistakes:

• Trying to assign logical array directly
• Using curly braces instead of parentheses
• Creating new struct without filtering