central, forward and backward differences

I wanted to make an input function for the user to add function and then the the script derives that function and then executes the rest of the code however i cannot get it to make an input function i will state where the errors are when i make an input

inp=input('function: ');


x=linspace(0,pi/2,10);
syms x; %error
y=inp; %error
dy=diff(y); %error  
dydx_analytical=dy; 
dydx_approx=diff(y)./diff(x);   %error
dydx_approx(length(x))=NaN;
percent_error=(dydx_analytical-dydx_approx)./dydx_analytical*100;
table=[x; dydx_analytical;dydx_approx;percent_error];   %error
disp('Forward Difference Approximation of the derivative sin(x)' )
disp(' x                dy/dx            dy/dx          %error')
disp('                           forward approximation ')
fprintf('%8.4f\t%8.4f\t%8.4f\t%8.4f\n', table)

plot(x,dydx_approx,'s--')
hold on
plot(x,dydx_analytical)
hold off
legend('Forward Difference','Analytical') 

[darova]

You declared x as numeric array then you are trying to mke it symbolic

x=linspace(0,pi/2,10);
syms x; %error

Can you show the way you input the function?