Compilare: user.cpp: In function ‘int main()’: user.cpp:24:36: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for( size_t middle = 0; middle < n ; ++middle ) ~~~~~~~^~~ user.cpp:25:30: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for( size_t x = 0; x < n; ++x ) ~~^~~ user.cpp:26:34: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for( size_t y = 0; y < n; ++y ) ~~^~~