Writing text files (writetable, fprintf) in MATLAB - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this fprintf code?

Consider the following MATLAB code that writes formatted text to a file. What will be the content of the file after running this code?

MATLAB

fid = fopen('output.txt', 'w');
fprintf(fid, 'Value: %d\n', 42);
fclose(fid);
file_content = fileread('output.txt');
disp(file_content);

A

Value: %d

B 24 :eulaV

C

Value: 42

D Error: File not found

💡 Hint

Remember that fprintf with '%d' replaces the placeholder with the integer value and '\n' adds a new line.

The fprintf function writes 'Value: 42' followed by a newline character to the file. The fileread reads the file content including the newline, so the displayed content includes the line break.

❓ Predict Output

intermediate

What does writetable write to the file?

Given this MATLAB code, what will be the content of 'data.csv' after execution?

MATLAB

T = table([1;2;3], {'A';'B';'C'}, 'VariableNames', {'ID', 'Letter'});
writetable(T, 'data.csv');
content = fileread('data.csv');
disp(content);

A Error: VariableNames not supported

B

ID,Letter
1,A
2,B
3,C

C

ID Letter
1 A
2 B
3 C

D

1,A
2,B
3,C

💡 Hint

writetable writes variable names as headers by default and separates values with commas in CSV format.

The writetable function writes the table with headers separated by commas and each row on a new line, so the file content includes the header line 'ID,Letter' followed by the data rows.

🔧 Debug

advanced

Why does this fprintf code produce an error?

Examine the code below. Why does it cause an error when run?

MATLAB

fid = fopen('test.txt', 'w');
fprintf(fid, 'Number: %d %f\n', 5);
fclose(fid);

A fprintf expects two values for '%d' and '%f' but only one is provided, causing an error.

B fopen failed to open the file, so fprintf errors out.

C The format string is invalid because '%f' cannot be used with fprintf.

D fclose is called before fprintf, causing an error.

💡 Hint

Check how many values fprintf expects based on the format string placeholders.

The format string '%d %f\n' requires two values, but only one (5) is provided. This mismatch causes fprintf to error.

📝 Syntax

advanced

Which option correctly writes a table without row names?

You want to write a table to a CSV file without including row names. Which code does this correctly?

MATLAB

T = table([10;20], {'X';'Y'}, 'VariableNames', {'Num', 'Char'});

A writetable(T, 'file.csv', 'RowNames', false);

B writetable(T, 'file.csv', 'WriteRowNames', true);

C writetable(T, 'file.csv', 'IncludeRowNames', false);

D writetable(T, 'file.csv', 'WriteRowNames', false);

💡 Hint

Check the exact parameter name for controlling row names in writetable.

The correct parameter to exclude row names is 'WriteRowNames' set to false. Other options use incorrect parameter names or values.

🚀 Application

expert

How many lines are written by this fprintf loop?

This MATLAB code writes lines to a file. How many lines will the file contain after running?

MATLAB

fid = fopen('log.txt', 'w');
for i = 1:5
    fprintf(fid, 'Line %d\n', i);
end
fclose(fid);
content = fileread('log.txt');
lines = count(content, '\n');

A 5

B 6

C 4

D 1

💡 Hint

Each fprintf call writes one line ending with '\n'. Count how many times the loop runs.

The loop runs 5 times, each writing one line with a newline character, so the file has 5 lines.