Why reading and writing data is fundamental in MATLAB - Challenge Your Understanding

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this MATLAB code reading a file?

Consider the following MATLAB code that reads data from a text file named data.txt containing numbers:

fid = fopen('data.txt', 'r');
data = fscanf(fid, '%d');
fclose(fid);
disp(data);

If data.txt contains the numbers 10 20 30 40 separated by spaces, what will be displayed?

MATLAB

fid = fopen('data.txt', 'r');
data = fscanf(fid, '%d');
fclose(fid);
disp(data);

A [10 20 30 40]

B [10 20 30 40 0]

C Error: File not found

D [10; 20; 30; 40]

💡 Hint

Remember that fscanf reads data column-wise and returns a column vector by default.

The fscanf function reads the numbers as integers and returns a column vector, so the output is a 4x1 vector displayed as:

10
20
30
40

❓ Predict Output

intermediate

What happens when writing data to a file in MATLAB?

Given this MATLAB code snippet:

fid = fopen('output.txt', 'w');
fprintf(fid, '%0.2f\n', [1.234, 5.678, 9.1011]);
fclose(fid);

What will be the content of output.txt after running this code?

MATLAB

fid = fopen('output.txt', 'w');
fprintf(fid, '%0.2f\n', [1.234, 5.678, 9.1011]);
fclose(fid);

A 1.23\n5.68\n9.10\n

B 1.234 5.678 9.1011

C 1.23 5.68 9.10

D Error: Invalid format specifier

💡 Hint

Look at the format string and how fprintf writes each number.

The format %0.2f\n writes each number with two decimals followed by a newline, so the file will have three lines:

1.23
5.68
9.10

❓ Predict Output

advanced

What is the output of this MATLAB code reading mixed data?

Analyze this MATLAB code snippet:

fid = fopen('mixed.txt', 'r');
data = textscan(fid, '%s %f');
fclose(fid);
disp(data{2});

If mixed.txt contains:

apple 10
banana 20
cherry 30

What will be displayed?

MATLAB

fid = fopen('mixed.txt', 'r');
data = textscan(fid, '%s %f');
fclose(fid);
disp(data{2});

A ['apple'; 'banana'; 'cherry']

B [10; 20; 30]

C ["apple", "banana", "cherry"]

D Error: Invalid format specifier

💡 Hint

textscan returns a cell array; data{2} accesses the numeric column.

The second element of the cell array data{2} contains the numeric values as a column vector, so the output is:

10
20
30

❓ Predict Output

advanced

What error does this MATLAB code produce when reading a non-existent file?

Consider this MATLAB code:

fid = fopen('nofile.txt', 'r');
data = fscanf(fid, '%d');
fclose(fid);

What error or output will occur?

MATLAB

fid = fopen('nofile.txt', 'r');
data = fscanf(fid, '%d');
fclose(fid);

A fid equals -1, fscanf returns empty, fclose runs without error

B fid equals -1, fscanf returns empty, fclose errors

C fid equals -1, fscanf errors, fclose errors

D Error: File not found

💡 Hint

Check what fopen returns when the file does not exist and how fscanf and fclose behave.

fopen returns -1 if the file does not exist. fscanf returns empty without error. fclose(-1) returns -1 but does not throw an error. So no error is thrown, but fid is -1 and data is empty.

🧠 Conceptual

expert

Why is reading and writing data fundamental in programming?

Which of the following best explains why reading and writing data is fundamental in programming?

A Because data reading and writing automatically optimizes program speed.

B Because reading and writing data is the only way to create variables in memory.

C Because programs need to interact with external information sources to be useful and persistent.

D Because all programming languages require manual file handling to run any code.

💡 Hint

Think about why programs need input and output beyond just running code.

Reading and writing data allows programs to get input from users or other systems and save results for later use, making programs practical and meaningful.