error with my symbolic objects and fprintf

I am quite inexperienced with matlab, I am getting this error when I run:

Error using fprintf
Function is not defined for 'sym' inputs.
Error in colebrook (line 22)
    fprintf('%3i %12.8s %12.8s %12.8s\n',count, x, dx, f)

function colebrook (f,Re,e)

syms e Re x;

df = diff(1/sqrt(x)+2*log(e/3.7+2.51/(Re*sqrt(x))),x);

Tol = .001;

x=.02;

count = 0;

dx = 1;

fprintf('step      x           dx           f(x)\n')

fprintf('----  -----------  ---------    ----------\n')

fprintf('%3i %12.8f %12.8f %12.8f\n',count, x, dx, f)

xVec=x;fVec=f;%eVec=e;ReVec=Re;

while (dx > Tol || abs(f)>Tol)

    count = count + 1;

    xnew = x - (f/df);

    dx=abs(x-xnew);     

    x = xnew;

    f =  (1/sqrt(x)+2*log(e/3.7+2.51/(Re*sqrt(x))));

    fprintf('here');

    e = char (e);

    Re = char (Re);

    x = char (x);

    fprintf('%3i %12.8s %12.8s %12.8s\n',count, x, dx, f)

end

Answer 1

[Walter Roberson]

xnew = x - double(f(x)/df(x));

[Qutyba Shteyat]

Thankssssssssssss