i got error "Undefined variable "handles" or function "handles.slider1". plz help me

threshold = get(handles.slider1,'Value');  
t = get(handles.slider1,'value');%position of X slider
  set(handles.text1,'String', num2str(x));            %read the value of threshold from GUI slider
handles.t=t;
guidata(hObject,handles)
%start a for loop that equal the number of images usually infinity
for l = 1:inf

      flag=get(handles.togglebutton1,'value');        %This flag is used to check if stop button was pressed
      if (flag==1)
          a=a+1;

          v= getsnapshot(vobj);                       %read image from camera and save it in variable v
          w= getsnapshot(vobj);                       %read image from camera and save it in variable w

          x= rgb2gray (v);                            %convert image to gray scale
          y= rgb2gray(w);                             %convert image to gray scale

          z = imabsdiff(x,y);                         %get absolute diffrence between both images
          zz= sum(z,1);                               %calculate SAD
          zzz= sum(zz)/ 76800;                        %scale the value of SAD by dividing by number of pixels

          h(a) = zzz;                                 %put values of SAD in array h

          hh=[ h(a-1) h(a) ];                         %calculate variance value
          var_value=var(hh,1);

          var_values(a)=var_value;                    %put values of variance in array var_value