Compilare: main.cpp: In lambda function: main.cpp:21:38: warning: narrowing conversion of '(& mat1)->std::vector<_Tp, _Alloc>::size<std::vector<long long int>, std::allocator<std::vector<long long int> > >()' from 'std::vector<std::vector<long long int> >::size_type {aka long unsigned int}' to 'int' inside { } [-Wnarrowing] const int nr_lines1{mat1.size()}, nr_cols1{mat1.front().size()}, nr_cols2{mat2.front().size()}; ~~~~~~~~~^~ main.cpp:21:69: warning: narrowing conversion of '(&(& mat1)->std::vector<_Tp, _Alloc>::front<std::vector<long long int>, std::allocator<std::vector<long long int> > >())->std::vector<_Tp, _Alloc>::size<long long int, std::allocator<long long int> >()' from 'std::vector<long long int>::size_type {aka long unsigned int}' to 'int' inside { } [-Wnarrowing] const int nr_lines1{mat1.size()}, nr_cols1{mat1.front().size()}, nr_cols2{mat2.front().size()}; ~~~~~~~~~~~~~~~~~^~ main.cpp:21:100: warning: narrowing conversion of '(&(& mat2)->std::vector<_Tp, _Alloc>::front<std::vector<long long int>, std::allocator<std::vector<long long int> > >())->std::vector<_Tp, _Alloc>::size<long long int, std::allocator<long long int> >()' from 'std::vector<long long int>::size_type {aka long unsigned int}' to 'int' inside { } [-Wnarrowing] const int nr_lines1{mat1.size()}, nr_cols1{mat1.front().size()}, nr_cols2{mat2.front().size()}; ~~~~~~~~~~~~~~~~~^~ main.cpp: In lambda function: main.cpp:38:36: warning: narrowing conversion of 'mat.std::vector<_Tp, _Alloc>::size<std::vector<long long int>, std::allocator<std::vector<long long int> > >()' from 'std::vector<std::vector<long long int> >::size_type {aka long unsigned int}' to 'int' inside { } [-Wnarrowing] const int nr_lines{mat.size()}; ~~~~~~~~^~