Why I can't run this coding?

syms q1  t 
%q1(t)
h=q1
q1_of_t=sym('q1(t)')
h1=subs(h,q1,q1_of_t)
%diff q1(t),diff twice q1(t)
diff_q1t=diff(h1,t);
diff_q1t2=diff(diff_q1t,t);

% t is for time
% q1_of_t=sym('q1(t)') - can't run in Matlab online but actually 3 years
% ago its can run in dowloaded matlab

Answer 1

[VBBV]

syms q1(t)  t 
%q1(t)
h=q1

h(t) = 

q1_of_t=symfun('q1(t)',t)

q1_of_t(t) = 

h1=subs(h,q1,q1_of_t)

h1(t) = 

%diff q1(t),diff twice q1(t)
diff_q1t=diff(h1,t);
diff_q1t2=diff(diff_q1t,t)

diff_q1t2(t) = 

% t is for time
% q1_of_t=sym('q1(t)') - can't run in Matlab online but actually 3 years
% ago its can run in dowloaded matlab

[VBBV]

use symfun

q1_of_t=symfun('q1(t)',t)

instead of

q1_of_t=sym('q1(t)')