Plot of any equation using GUI

I want to made a plotter using GUI. For that purposes i tried to write the expression.Then converting this expression(string) into symbolic expression and plotting it.After that i tried the following code.

Basically i want to plot anytype of implicit and explicit equation.

But it didn't work properly.what to do?

% --- Executes on button press in Plott.
function Plott_Callback(hObject, eventdata, handles)
% hObject    handle to Plott (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
strr=get(handles.screen,'string');
syms x y;
axes(handles.axes1);
x=0:0.1:10;
y=str2sym(strr);
fplot(y,[-10 20]);
guidata(hObject,handles);