integration

[davidaholic]

******urgent

i have a project to make a integral with matlab
when i make a code i have an error. this is the code

f = str2double(get(edit1,'string'));
a = str2double(get(edit2,'string'));
b = str2double(get(edit3,'string'

chose = get(popup1,'value');
switch pilihan
case 1
f=@x;
case 2
f=@y;
end;

f=quad(f,a,b);

if a >= b
disp('you.re wrong!!!!!!');
end

and i get error in

??? Undefined function or method 'x' for input arguments of type 'double'.

Error in ==> quad at 77
y = f(x, varargin{:});

Error in ==> luas1b at 13
f=quad(f,a,b);

??? Error while evaluating uicontrol Callback

and i want to ask 1 more if i want to plot with unknown function do you know what is the code