X(X==0)=nan; % flag zero locations
d=diff(X); % compute difference w/ flagged
d(isnan(d))=0; % replace NaN in output if desired
For the sample given
>> Y=X;Y(Y==0)=nan;
>> d=diff(Y); d(isnan(d))=0
d =
0 1 0 0 0 0 8
>>
