Explanation
strcat concatenates strings. However num2cell([1:100]') are not strings, they are numeric scalars in a cell array. Where is the string conversion? There isn't any! So strcat thinks that those numeric values are the characters' values, and returns the equivalent character corresponding to each value (some characters are not printable):
>> char(32:100)
ans = !"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcd
Solution
To generate strings of those numeric values, try this:
tmp = arrayfun(@num2str,[1:100].','UniformOutput',false)
and also note that you do not need to use repmat or to put the strings 'sample' and '_' into cell arrays: this is a total waste of time and makes the intent of the code much harder to understand. Don't make code more complicated than it needs to be, just do this:
out = strcat('sample_',tmp)
Or you could get rid of the strcat altogether, and just do it using one arrayfun call:
arrayfun(@(n)sprintf('sample_%d',n), [1:100], 'UniformOutput',false)
