Dynamic field names in MATLAB - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this code using dynamic field names?

Consider the following MATLAB code that uses dynamic field names in a struct. What will be the output displayed?

MATLAB

fieldName = 'score';
student.(fieldName) = 95;
disp(student.score);

A 95

B Error: Undefined function or variable 'score'.

C student.score

D 0

💡 Hint

Dynamic field names allow you to use a variable as the field name in a struct.

The variable 'fieldName' holds the string 'score'. Using student.(fieldName) = 95; sets the field 'score' of struct 'student' to 95. Displaying student.score prints 95.

❓ Predict Output

intermediate

What does this code print when using dynamic field names with a loop?

Look at this MATLAB code snippet. What will be the output after running it?

MATLAB

fields = {'a', 'b', 'c'};
for i = 1:length(fields)
    data.(fields{i}) = i*10;
end
disp(data.b);

A 20

B b

C 0

D Error: Index exceeds matrix dimensions.

💡 Hint

Each field in 'data' is set to i*10 where i is the loop index.

The loop assigns data.a = 10, data.b = 20, data.c = 30. Displaying data.b prints 20.

🔧 Debug

advanced

Identify the error in this dynamic field name usage

This MATLAB code tries to assign a value using a dynamic field name but causes an error. What is the cause?

MATLAB

field = 123;
record.(field) = 'value';

A Error because 'record' is not initialized

B Error because 'value' is not defined

C No error, code runs fine

D Error because field name must be a string or character vector

💡 Hint

Field names in structs must be text, not numbers.

In MATLAB, struct field names must be strings or character vectors. Using a numeric value as a field name causes an error.

📝 Syntax

advanced

Which option correctly creates a struct with dynamic field names?

Select the MATLAB code snippet that correctly creates a struct with dynamic field names from variables 'f1' and 'f2'.

A f1 = 'name'; f2 = 'age'; person.f1 = 'Alice'; person.f2 = 30;

B f1 = 'name'; f2 = 'age'; person.(f1) = 'Alice'; person.(f2) = 30;

C f1 = 'name'; f2 = 'age'; person{f1} = 'Alice'; person{f2} = 30;

D f1 = 'name'; f2 = 'age'; person.(f1, f2) = {'Alice', 30};

💡 Hint

Use parentheses and dot notation with a string variable for dynamic field names.

Option B uses the correct syntax: person.(f1) assigns to the field named by the string in f1. Option B assigns to fields literally named 'f1' and 'f2'. Option B uses curly braces which is invalid for struct fields. Option B tries to assign multiple fields at once which is invalid syntax.

🚀 Application

expert

How many fields does the struct have after this code runs?

Given the following MATLAB code, how many fields does the struct 'info' contain at the end?

MATLAB

fields = {'x', 'y', 'x', 'z'};
info = struct();
for k = 1:length(fields)
    info.(fields{k}) = k;
end

A 2

B 4

C 3

D 1

💡 Hint

Struct fields must be unique; repeated field names overwrite previous values.

The field 'x' appears twice. The second assignment overwrites the first. The final fields are 'x', 'y', and 'z', so total 3 fields.