MATLAB: #what is the problem in the code so that it is not accepted?

circle problem

function [area,cf]=circle(r)
cf=2*pi*r;
area=pi*r*r;
end

That code is accepted. But you need to store it in circle.m, and you need to pass a value on the command line:

>> [A,B] = circle(7)
A =
            153.9380400259
B =
          43.9822971502571

function cercle(r)
x=-r:.01:r
y=sqrt(r^2-x.^2)
hold on;
plot(x,y);
plot(x,-y)

call the function

 cercle(5)

You probably want

     r=getappdata(0,'Variable1') % get the value of radius from circle UI

as the second parameter to getappdata is a string.