Compilare: main.cpp: In function 'matrix multiply(matrix, matrix)': main.cpp:72:27: warning: comparison of integer expressions of different signedness: 'long long int' and 'std::vector<std::vector<long long int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare] 72 | for (int i = 0; i < a.size(); ++i) { | ~~^~~~~~~~~~ main.cpp:73:35: warning: comparison of integer expressions of different signedness: 'long long int' and 'std::vector<long long int>::size_type' {aka 'long unsigned int'} [-Wsign-compare] 73 | for (int j = 0; j < b[0].size(); ++j) { | ~~^~~~~~~~~~~~~ main.cpp:74:43: warning: comparison of integer expressions of different signedness: 'long long int' and 'std::vector<long long int>::size_type' {aka 'long unsigned int'} [-Wsign-compare] 74 | for (int k = 0; k < a[0].size(); ++k) { | ~~^~~~~~~~~~~~~ main.cpp: In function 'matrix pow(matrix, long long int)': main.cpp:86:27: warning: comparison of integer expressions of different signedness: 'long long int' and 'std::vector<std::vector<long long int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare] 86 | for (int i = 0; i < a.size(); ++i) { | ~~^~~~~~~~~~