For a start you might like to read this (if you want to write better code, then it can help you):
And then to solve your problem you do not need to write lots of if-s or use eval, in fact you can do solve your quite simply by creating a cell array of indices and using that to generate a comma-separated list:
>> X = randi(9,1,2,3,4);
>> C = {':',':',2,':'};
>> X(C{:})
ans(:,:,1,1) =
1 1
ans(:,:,1,2) =
8 2
ans(:,:,1,3) =
3 8
ans(:,:,1,4) =
2 4
Another alternative is to call subsref directly. The function subsref is what MATLAB uses to index into variables, but you can also call it directly. All you need to do is create a suitable structure input, it is not that hard but you should play around with it to understand how it works. For example:
>> subsref(X,substruct('()',C))
ans(:,:,1,1) =
1 1
ans(:,:,1,2) =
8 2
ans(:,:,1,3) =
3 8
ans(:,:,1,4) =
2 4
Clearly it is pretty trivial to construct that cell array: something like this (untested):
C = repmat({':'},1,totdim);
C{ixdim} = ix;
