Structures and field access in MATLAB - Step-by-Step Execution

Concept Flow - Structures and field access

Create structure with fields

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Access field using dot notation

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Read or modify field value

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Use updated structure or field value

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End

This flow shows how to create a structure, access its fields using dot notation, read or change values, and then use the updated structure.

Execution Sample

MATLAB

person.name = 'Alice';
person.age = 30;
disp(person.name);
person.age = 31;
disp(person.age);

This code creates a structure 'person' with fields 'name' and 'age', displays the name, updates the age, and then displays the new age.

Execution Table

Step	Action	Structure State	Output
1	Create field 'name' with value 'Alice'	person.name = 'Alice'
2	Create field 'age' with value 30	person.name = 'Alice', person.age = 30
3	Display person.name	person.name = 'Alice', person.age = 30	Alice
4	Update person.age to 31	person.name = 'Alice', person.age = 31
5	Display person.age	person.name = 'Alice', person.age = 31	31
6	End of code	person.name = 'Alice', person.age = 31

💡 All lines executed; structure fields accessed and updated successfully.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 4	Final
person.name	undefined	'Alice'	'Alice'	'Alice'	'Alice'
person.age	undefined	undefined	30	31	31

Key Moments - 3 Insights

Why do we use dot notation like person.name to access fields?

Dot notation specifies which field inside the structure we want. See execution_table step 3 where person.name is accessed to display 'Alice'.

What happens if we try to access a field that doesn't exist?

MATLAB gives an error because the field is not defined. In this example, all fields exist as shown in variable_tracker.

How do we update a field value inside a structure?

Assign a new value using dot notation, like person.age = 31 in step 4 of execution_table.

Visual Quiz - 3 Questions

Look at the execution_table at step 3, what is the output when displaying person.name?

A "Alice"

B "30"

C "person"

D Error

💡 Hint

Check the Output column at step 3 in execution_table.

At which step does person.age get updated to 31?

A Step 2

B Step 3

C Step 4

D Step 5

💡 Hint

Look at the Action column in execution_table where the age field changes.

If we tried to display person.height (not defined), what would happen?

A Displays empty string

B Error: Field 'height' does not exist

C Displays 0

D Displays 'height'

💡 Hint

Refer to key_moments about accessing undefined fields.

Concept Snapshot

Structure creation: s.field = value
Access field: s.field
Update field: s.field = new_value
Fields hold data of any type
Accessing undefined field causes error

Full Transcript

This example shows how to create a MATLAB structure named 'person' with fields 'name' and 'age'. We assign 'Alice' to person.name and 30 to person.age. Using dot notation, we display person.name which outputs 'Alice'. Then we update person.age to 31 and display it, outputting 31. Dot notation is used to access or modify fields inside the structure. Trying to access a field that does not exist will cause an error. The variable tracker shows how the fields change after each step. This helps beginners understand how structures store related data and how to work with their fields.