matlab loop through folder

 function [ flag ] = CropAll( folder_name,h )  
 files=dir(strcat(folder_name,'/*.png'));  
 for i=1:numel(files)  
   file_name=files(i).name;  
   img=imread([folder_name,'/',file_name]);  
   img2=img(1:h,:,:);  
   imwrite(img2,[folder_name,'/',file_name]);  
 end  
 flag=1;  
 end