Workspace and variable management in MATLAB - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this MATLAB code snippet?

Consider the following MATLAB commands executed in order:

clear all
x = 5;
y = 10;
clear x;
z = exist('x', 'var');

What is the value of z after running this code?

MATLAB

clear all
x = 5;
y = 10;
clear x;
z = exist('x', 'var');

A 3

B 0

C 2

D 1

💡 Hint

Recall that clear x removes variable x from the workspace.

After clear x, variable x no longer exists in the workspace. The exist function returns 0 when the variable is not found.

❓ Predict Output

intermediate

How many variables remain after this code runs?

Given the following MATLAB commands:

a = 1;
b = 2;
c = 3;
clearvars -except a c;

How many variables are in the workspace after these commands?

MATLAB

a = 1;
b = 2;
c = 3;
clearvars -except a c;

A 2

B 1

C 3

D 0

💡 Hint

The clearvars -except command keeps only specified variables.

Only variables a and c remain after clearing all except these two.

🔧 Debug

advanced

Identify the error in this workspace management code

What error will this MATLAB code produce?

clear all
x = 10;
if exist('x')
    disp('x exists');
end

MATLAB

clear all
x = 10;
if exist('x')
    disp('x exists');
end

A No error, prints 'x exists'

B Syntax error: missing second argument in exist

C Runtime error: undefined variable 'x'

D Logical error: exist returns 0 even if variable exists

💡 Hint

exist('x') without a second argument is valid and returns 1 for variables in the workspace.

No error occurs. exist('x') returns 1 because x is a variable in the workspace, so 'x exists' is printed.

❓ Predict Output

advanced

What is the output of this variable clearing sequence?

Consider this MATLAB code:

a = 1;
b = 2;
c = 3;
clear a b
vars = who;

What does vars contain after running this code?

MATLAB

a = 1;
b = 2;
c = 3;
clear a b
vars = who;

A {}

B {'a', 'b', 'c'}

C {'a', 'b'}

D {'c'}

💡 Hint

The clear command removes specified variables from the workspace.

After clearing a and b, only c remains. The who function lists current variables.

🧠 Conceptual

expert

Which command will save only variables starting with 'data' to a file?

You have variables data1, data2, temp in your workspace. Which MATLAB command saves only variables starting with 'data' to myfile.mat?

A save('myfile.mat', '-except', 'temp')

B save('myfile.mat', 'data1', 'data2')

C save('myfile.mat', '-regexp', '^data')

D save('myfile.mat', 'data*')

💡 Hint

Use the -regexp option to save variables matching a pattern.

Option C uses -regexp '^data' to save all variables starting with 'data'. Option C is invalid syntax. Option C requires listing all variables explicitly. Option C is invalid because -except is not a valid save option.