As Jos says in his comment, most of your code is rather meaningless. In fact, if one was to be picky, one could find a fault with almost every line (use of clear all, close all, cd, unused variables, meaningless variable names, convoluted way of counting number of elements above threshold, using size to get the number of element of vectors, pointless num2str, lack of 't' option for fprintf, etc.)
I assume this should do what you want:
numfiles = 3;
threshold = 0.018;
linesabovethreshold = zeros(numfiles, 1);
for fileidx = 1:numfiles
filecontent = dlmread(sprintf('result_%d.txt, fileidx));
assert(iscolumn(filecontent), 'file number %d has more than one column', fileidx);
linesabovethreshold(fileidx) = sum(filecontent >= threshold);
end
dlmwrite('Fragility_44.txt', linesabovethreshold / 1000);
edit: forgot the 1000 division
