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    %% Change Structure Field Value  

%% 
% Create a structure with fields named |'File'| and |'Format'|. 
S = struct('File',{'myGraph'},'Format',[])  

%% 
% Short-circuit expressions are useful in |if| statements when you want
% multiple conditions to be true. The conditions can build on one another
% in such a way that it only makes sense to evaluate the second expression
% if the first expression is true. 
%
% Specify an |if| statement that executes only when |S| contains an empty
% field named |'Format'|. 
if isfield(S,'Format') && isempty(S.Format)
  S.Format = '.png';
end 
S 

%%
% The first condition tests if |'Format'| is the name of a field in
% structure |S|. The second statement then tests whether the |Format| field
% is empty. The truth of the second condition depends on the first. The
% second condition can never be true if the first condition is not true.
% Since |S| has an empty field named |'Format'|, the body statement
% executes and assigns |S.Format| the value |'.png'|.