String searching (contains, strfind) in MATLAB - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of strfind with multiple occurrences

What is the output of this MATLAB code?

str = 'banana';
idx = strfind(str, 'an');
disp(idx);

MATLAB

str = 'banana';
idx = strfind(str, 'an');
disp(idx);

A [1 3]

B [2 4]

C [2 3 4]

D []

💡 Hint

Remember strfind returns starting indices of the substring occurrences.

The substring 'an' appears twice in 'banana': starting at positions 2 and 4.

❓ Predict Output

intermediate

Using contains to check substring presence

What does this MATLAB code output?

str = 'Hello World';
tf = contains(str, 'world');
disp(tf);

MATLAB

str = 'Hello World';
tf = contains(str, 'world');
disp(tf);

A 1

B []

C 0

D Error: case sensitivity

💡 Hint

contains is case sensitive by default.

The substring 'world' (lowercase) is not found in 'Hello World' (capital W), so contains returns false (0).

❓ Predict Output

advanced

Case-insensitive contains usage

What is the output of this MATLAB code?

str = 'Data Science';
tf = contains(str, 'SCIENCE', 'IgnoreCase', true);
disp(tf);

MATLAB

str = 'Data Science';
tf = contains(str, 'SCIENCE', 'IgnoreCase', true);
disp(tf);

A 0

B []

C Error: Invalid parameter

D 1

💡 Hint

Check the 'IgnoreCase' option in contains.

With 'IgnoreCase' set to true, contains finds 'SCIENCE' in 'Data Science' ignoring case, so returns true (1).

❓ Predict Output

advanced

strfind with empty substring

What does this MATLAB code output?

str = 'example';
idx = strfind(str, '');
disp(idx);

MATLAB

str = 'example';
idx = strfind(str, '');
disp(idx);

A [1 2 3 4 5 6 7 8]

B []

C [1]

D Error: Empty substring not allowed

💡 Hint

Think about how strfind treats empty strings.

strfind returns all indices from 1 to length(str)+1 when searching for an empty substring.

🧠 Conceptual

expert

Difference between contains and strfind outputs

Which statement correctly describes the difference between MATLAB's contains and strfind functions when searching for a substring?

A contains returns logical true/false indicating presence; strfind returns indices of occurrences.

B contains returns indices of occurrences; strfind returns logical true/false.

C Both return indices but contains is case-insensitive by default.

D Both return logical true/false but strfind is faster.

💡 Hint

Think about what each function returns as output type.

contains returns a logical value true or false if substring is found; strfind returns the starting indices of each occurrence.