This works fine for me:
for k1 = 1:n-1
c(k1,:) = blanks(n*n);
Variable ‘c’ is listed as a [3 x 16] character array.
The index ‘i’ may be the problem. Please don't use ‘i’ or ‘j’ for indexing, since MATLAB uses them for its imaginary operators.
If that's not the problem, did you use ‘c’ somewhere earlier in you code as a constant or as vector or as a smaller matrix?