Compilare: main.cpp: In function 'int main()': main.cpp:37:24: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for ( k = 0; k < vec[i].size ( ); k++ ){ ~~^~~~~~~~~~~~~~~~~ main.cpp:42:28: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for ( k = 0; k < vec[j].size ( ); k++ ){ ~~^~~~~~~~~~~~~~~~~ main.cpp:60:24: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for ( k = 0; k < vec[i].size ( ); k++ ){ ~~^~~~~~~~~~~~~~~~~