Structure arrays in MATLAB - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of accessing a field in a structure array?

Consider the following MATLAB code:

students(1).name = 'Alice';
students(1).age = 21;
students(2).name = 'Bob';
students(2).age = 22;

result = {students.name};

What is the value of result after running this code?

MATLAB

students(1).name = 'Alice';
students(1).age = 21;
students(2).name = 'Bob';
students(2).age = 22;

result = {students.name};

A {'Alice'; 'Bob'}

B ['Alice', 'Bob']

C ['Alice'; 'Bob']

D {'Alice', 'Bob'}

💡 Hint

Remember that curly braces {} create cell arrays in MATLAB.

Using {students.name} collects the name fields from each element of the structure array into a cell array. So result is a 1x2 cell array containing 'Alice' and 'Bob'.

❓ Predict Output

intermediate

What is the size of a structure array after assignment?

Given this MATLAB code:

data(3).value = 0;
data(1).value = 10;
data(2).value = 20;

What is the size of data after these assignments?

MATLAB

data(3).value = 0;
data(1).value = 10;
data(2).value = 20;

A 3x1 structure array

B 1x2 structure array

C 1x3 structure array

D 3x3 structure array

💡 Hint

Assigning to data(3) creates elements 1 to 3 in a row vector by default.

In MATLAB, assigning to data(3) creates a 1x3 structure array. The default shape is a row vector unless specified otherwise.

🔧 Debug

advanced

Why does this code produce an error when accessing a field?

Examine this MATLAB code:

info(1).name = 'John';
info(2).age = 30;

names = {info.name};

What error will occur when running this code?

MATLAB

info(1).name = 'John';
info(2).age = 30;
names = {info.name};

A Field 'name' does not exist for index 2.

B Syntax error: missing semicolon.

C names is an empty cell array {}.

D No error; names = {'John', ''}.

💡 Hint

Check if all elements of the structure array have the field name.

Because info(2) does not have the field name, trying to access info.name causes an error.

🧠 Conceptual

advanced

How to add a new field to all elements of a structure array?

You have a structure array records with 5 elements. You want to add a new field status with value 'active' to every element. Which code does this correctly?

A records.status = 'active';

B

for i = 1:length(records)
  records(i).status = 'active';
end

C records(:).status = 'active';

D records.status(:) = 'active';

💡 Hint

Think about how MATLAB assigns fields to structure arrays element-wise.

Only option B assigns the new field status to each element individually. Option B creates a single field for the whole array, which is invalid. Options C and D are syntactically incorrect.

❓ Predict Output

expert

What is the output of this nested structure array code?

Consider this MATLAB code:

team(1).player.name = 'Anna';
team(1).player.score = 10;
team(2).player.name = 'Ben';
team(2).player.score = 15;

scores = [team.player.score];

What is the value of scores after running this code?

MATLAB

team(1).player.name = 'Anna';
team(1).player.score = 10;
team(2).player.name = 'Ben';
team(2).player.score = 15;

scores = [team.player.score];

A [10 15]

B [[10] [15]]

C [10; 15]

D Error: Cannot concatenate nested fields directly.

💡 Hint

Accessing nested fields in structure arrays returns arrays of those values.

Accessing team.player.score collects the score fields from each nested player structure into a numeric array. So scores is [10 15].