error in line1and 4

Calculate the response function using the equation of motion:
omega_n = sqrt(k / m); % natural frequency
zeta = c / (2 * sqrt(m * k)); % damping ratio
omega_n = omega_n * sqrt(1 - zeta^2); % damped natural frequency
Calculate the response function using the equation of motion:
omega_n = sqrt(k / m); % natural frequency
zeta = c / (2 * sqrt(m * k)); % damping ratio
omega_d = omega_n * sqrt(1 - zeta^2); % damped natural frequency
figure;
plot(t, X);
xlabel('Time (s)');
ylabel('Displacement (m)');
title('Response of Mass-Spring-Damper System');
grid on;

Answer 1

[Chunru]

Those are comments which shoud start with %

% Calculate the response function using the equation of motion:
omega_n = sqrt(k / m); % natural frequency

Unrecognized function or variable 'k'.

zeta = c / (2 * sqrt(m * k)); % damping ratio
omega_n = omega_n * sqrt(1 - zeta^2); % damped natural frequency
% Calculate the response function using the equation of motion:
omega_n = sqrt(k / m); % natural frequency
zeta = c / (2 * sqrt(m * k)); % damping ratio
omega_d = omega_n * sqrt(1 - zeta^2); % damped natural frequency
figure;
plot(t, X);
xlabel('Time (s)');
ylabel('Displacement (m)');
title('Response of Mass-Spring-Damper System');
grid on;

[firas]

it says vakue assigned to variable might be unsured (omega_n);

omega_n = omega_n * sqrt(1 - zeta^2); % damped natural frequency

[Torsten]

It means that you defined a variable, but you didn't use this variable in the sequel. Thus deleting the line where you defined the variable would not change anything in the results from the code - usually an indicator that you made a mistake.