Type checking (class, isa) in MATLAB - Step-by-Step Execution

Concept Flow - Type checking (class, isa)

Start with variable

↓

Check type with class()

↓

Compare class string

↓

Match

↓

Do action

↓

Start with variable

↓

Check type with isa()

↓

isa returns true or false

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True

↓

Do action

First, get the variable's type using class() or check type inheritance with isa(). Then decide what to do based on the result.

Execution Sample

MATLAB

x = 5;
if strcmp(class(x), 'double')
    disp('x is a double')
end

if isa(x, 'double')
    disp('x is a double (isa)')
end

This code checks if variable x is of type double using class() and isa(), then prints messages.

Execution Table

Step	Action	Evaluation	Result	Output
1	Assign x = 5	x = 5	x is double (numeric)
2	Evaluate class(x)	class(5)	'double'
3	Compare class(x) == 'double'	strcmp(class(x), 'double')	true
4	If true, disp('x is a double')	true	display message	x is a double
5	Evaluate isa(x, 'double')	isa(5, 'double')	true
6	If true, disp('x is a double (isa)')	true	display message	x is a double (isa)
7	End	No more code	Execution stops

💡 Reached end of code, all checks done

Variable Tracker

Variable	Start	After Step 1	After Step 7
x	undefined	5	5

Key Moments - 2 Insights

Why do we use strcmp with class(x) instead of ==?

Because class(x) returns a string, and in MATLAB strings must be compared with strcmp, not ==. See execution_table row 3.

What is the difference between class() and isa()?

class() returns the exact type name as a string, while isa() checks if the variable is of a given type or inherits from it. See execution_table rows 2 and 5.

Visual Quiz - 3 Questions

Look at the execution table, what is the output after step 4?

A x is a double (isa)

B x is a double

C No output

D Error

💡 Hint

Check the Output column at step 4 in the execution_table

At which step does isa(x, 'double') get evaluated?

A Step 5

B Step 4

C Step 2

D Step 6

💡 Hint

Look at the Action column for isa() evaluation in the execution_table

If x was a string 'hello', what would strcmp(class(x), 'double') return?

A error

B true

C false

D depends on isa

💡 Hint

Recall class('hello') returns 'char', so strcmp('char', 'double') is false

Concept Snapshot

Type checking in MATLAB:
- Use class(var) to get exact type as string
- Compare with strcmp for equality
- Use isa(var, 'TypeName') to check type or inheritance
- isa returns true/false, class returns string
- Use these to control program flow based on variable type

Full Transcript

This example shows how MATLAB checks variable types using class() and isa(). First, variable x is assigned the value 5. Then class(x) returns 'double', which is compared to the string 'double' using strcmp. Since they match, the program prints 'x is a double'. Next, isa(x, 'double') checks if x is of type double or inherits from it, returning true, so it prints 'x is a double (isa)'. The execution table traces each step, showing variable values and outputs. Key points include using strcmp for string comparison and understanding the difference between class and isa. The visual quiz tests understanding of outputs and evaluation steps. This helps beginners see how MATLAB checks types step-by-step.