how to fprintf vectors of symbolic function with parentheses

for example: turev_s('x^2+y^2*sin(t)','t','x,y,t',[1 2 30])

I get an alert when I make the above example. How can I solve this problem?

Can not I show the value of "s" as fprintf?

function turev_s(x, y, d, r) 

f = sym(x);
n = length(symvar(f)); 

if n == 1
    s = diff(f,y);    
    sade = simplify(s)
    pretty(s)
    if r ~= 0
        sonuc = double(subs(f,{d},{r}));
    end
elseif n == 2
    s = diff(f,y);
    sade = simplify(s)
    pretty(s) 
    if r ~= 0
        sonuc = double(subs(f,{d},{r}));
    end
elseif n == 3
    s = diff(f,y);
    sade = simplify(s)
    pretty(s) 
    if r ~= 0
        sonuc = double(subs(f,{d},{r}));
    end
end
fprintf('Sonuc = %.4f\n',sonuc);
end

[Walter Roberson]

Duplicated by later https://www.mathworks.com/matlabcentral/answers/363947-warning-support-of-strings-that-are-not-valid-variable-names-or-define-a-number-will-be-removed-in