Compilare: main.cpp: In function 'int64_t calc(int, int)': main.cpp:14:17: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare] 14 | for(int f = 0;f < A[i][j].size(); ++f){ | ~~^~~~~~~~~~~~~~~~ main.cpp:18:13: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare] 18 | while(f < A[i][j].size() && A[i][j][f] >= '0' && A[i][j][f] <= '9'){ | ~~^~~~~~~~~~~~~~~~ main.cpp:21:10: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare] 21 | if(f < A[i][j].size()) | ~~^~~~~~~~~~~~~~~~ main.cpp:25:13: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare] 25 | while(f < A[i][j].size() && A[i][j][f] >= '0' && A[i][j][f] <= '9') | ~~^~~~~~~~~~~~~~~~