Dynamic field names in MATLAB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a structure with a dynamic field name.

MATLAB

fieldName = 'age';
person.[1] = 25;

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

A(fieldName)

BfieldName

C{fieldName}

DfieldName()

Attempts:

3 left

💡 Hint

Common Mistakes

Using dot notation without parentheses for dynamic field names.

Using curly braces instead of parentheses.

In MATLAB, dynamic field names are accessed using parentheses and the field name as a string: person.(fieldName).

2fill in blank

medium

Complete the code to read a dynamic field value from a structure.

MATLAB

field = 'score';
value = data.[1];

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

A{field}

Bfield

C(field)

D.field

Attempts:

3 left

💡 Hint

Common Mistakes

Using dot notation without parentheses.

Using curly braces instead of parentheses.

To access a dynamic field in MATLAB, use parentheses with the field name string: data.(field).

3fill in blank

hard

Fix the error in the code to correctly assign a value to a dynamic field.

MATLAB

fieldName = 'height';
person.[1] = 180;

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

A(fieldName)

BfieldName

C{fieldName}

D['fieldName']

Attempts:

3 left

💡 Hint

Common Mistakes

Using dot notation without parentheses.

Using curly braces or brackets instead of parentheses.

Dynamic field names require parentheses around the variable holding the field name string: person.(fieldName).

4fill in blank

hard

Fill both blanks to create a structure with dynamic field names and assign values.

MATLAB

fields = {'name', 'age'};
values = {'Alice', 30};
for i = 1:length(fields)
    person.[1] = values{i};
end

% Access the age field dynamically
ageValue = person.[2];

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

A(fields{i})

B(values{i})

C(fields{2})

D(fields)

Attempts:

3 left

💡 Hint

Common Mistakes

Using dot notation without parentheses inside the loop.

Accessing the field without parentheses.

Use person.(fields{i}) to assign values dynamically in the loop, and person.(fields{2}) to access the 'age' field.

5fill in blank

hard

Fill all three blanks to create a structure with dynamic fields, assign values, and check a condition.

MATLAB

fields = {'height', 'weight', 'age'};
values = [170, 65, 25];
for i = 1:length(fields)
    person.[1] = values(i);
end

if person.[2] > 20
    status = '[3]';
else
    status = 'young';
end

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

A(fields{i})

B(fields{3})

Cadult

Dage

Attempts:

3 left

💡 Hint

Common Mistakes

Using dot notation without parentheses.

Using wrong field name for the condition.

Forgetting to put quotes around the status string.

Assign values dynamically with person.(fields{i}), check the 'age' field with person.(fields{3}), and set status to 'adult' if age > 20.

Practice

1. What is the main purpose of using dynamic field names in MATLAB structures?

easy

A. To use variables as field names in structures

B. To create arrays with dynamic sizes

C. To perform matrix multiplication

D. To define functions inside structures

Solution

1. Step 1: Understand dynamic field names

   Dynamic field names allow using a variable to specify the name of a field in a structure.

2. Step 2: Identify the purpose

   This helps when field names are not fixed and need to be set or accessed dynamically during program execution.

3. Final Answer:

   To use variables as field names in structures -> Option A

4. Quick Check:

   Dynamic field names = variable field names [OK]

Hint: Dynamic field names use variables for field keys [OK]

Common Mistakes:

• Confusing dynamic fields with arrays
• Thinking dynamic fields define functions
• Mixing dynamic fields with matrix operations

2. Which of the following is the correct syntax to assign a value to a dynamic field name fname in a structure S?

easy

A. S.(fname) = 10;

B. S.fname = 10;

C. S{fname} = 10;

D. S[fname] = 10;

Solution

1. Step 1: Recall MATLAB syntax for dynamic fields

   Dynamic field names use parentheses and dot notation: structure.(variableName).

2. Step 2: Check each option

   S.(fname) = 10; uses S.(fname) which is correct syntax. Options A, C, and D are invalid for dynamic field names.

3. Final Answer:

   S.(fname) = 10; -> Option A

4. Quick Check:

   Use dot and parentheses for dynamic fields [OK]

Hint: Use S.(variable) to access dynamic fields [OK]

Common Mistakes:

• Using dot without parentheses for variable field
• Using curly braces or square brackets instead of dot
• Confusing cell or array indexing with struct fields

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

field = 'age';
S.(field) = 25;
disp(S.age);

medium

A. age

B. Empty output

C. Error: Undefined field 'age'

D. 25

Solution

1. Step 1: Assign dynamic field

   The variable field holds 'age'. Using S.(field) = 25; creates field 'age' with value 25 in structure S.

2. Step 2: Display the field value

   disp(S.age); prints the value of field 'age', which is 25.

3. Final Answer:

   25 -> Option D

4. Quick Check:

   Dynamic field 'age' = 25 [OK]

Hint: Dynamic field names create fields with variable keys [OK]

Common Mistakes:

• Expecting field name to be literal 'field'
• Confusing variable name with field name
• Not using parentheses for dynamic field assignment

4. Identify the error in the following MATLAB code snippet:

fname = 'score';
S.fname = 100;
disp(S.score);

medium

A. Variable fname is not defined

B. Missing semicolon after assignment

C. Using dot notation with variable name instead of dynamic field

D. disp function cannot display structure fields

Solution

1. Step 1: Analyze field assignment

   The code uses S.fname = 100; which creates a field literally named 'fname', not 'score'.

2. Step 2: Check display statement

   disp(S.score); tries to display field 'score' which does not exist, causing an error.

3. Final Answer:

   Using dot notation with variable name instead of dynamic field -> Option C

4. Quick Check:

   Use S.(fname) for dynamic fields [OK]

Hint: Use parentheses for dynamic field names to avoid errors [OK]

Common Mistakes:

• Using dot notation without parentheses for variable fields
• Assuming variable name becomes field name automatically
• Ignoring error from missing field access

5. Given a list of field names fields = {'name', 'age', 'score'} and values vals = {'Alice', 30, 95}, which code correctly creates a structure S with these dynamic fields and values?

hard

A. for i = 1:length(fields)
S{fields{i}} = vals{i};
end

B. for i = 1:length(fields)
S.(fields{i}) = vals{i};
end

C. for i = 1:length(fields)
S.fields{i} = vals{i};
end

D. for i = 1:length(fields)
S.(vals{i}) = fields{i};
end

Solution

1. Step 1: Understand dynamic assignment in loop

   We want to assign each field name from fields as a field in S with corresponding value from vals.

2. Step 2: Check each option

   for i = 1:length(fields) S.(fields{i}) = vals{i}; end uses S.(fields{i}) = vals{i}; which correctly assigns dynamic fields. Options A, B, and D use incorrect syntax or swap keys and values.

3. Final Answer:

   for i = 1:length(fields) S.(fields{i}) = vals{i}; end -> Option B

4. Quick Check:

   Loop with S.(fields{i}) = vals{i} assigns dynamic fields [OK]

Hint: Use S.(fields{i}) = vals{i} in loop for dynamic fields [OK]

Common Mistakes:

• Using dot notation without parentheses inside loop
• Confusing cell array indexing with struct field access
• Swapping keys and values in assignment