Compilare: user.cpp: In function ‘int main()’: user.cpp:127:46: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int j = 0; j < stations[i].size(); ++ j) ^ user.cpp:128:54: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int k = j + 1; k < stations[i].size(); ++ k) { ^ user.cpp:136:50: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int k = 0; k < stations[i].size(); ++ k) ^ user.cpp:137:54: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int l = 0; l < stations[j].size(); ++ l) { ^ user.cpp:161:62: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int z = 0; z < stations[i].size(); ++ z) { ^ user.cpp:171:62: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int z = 0; z < stations[j].size(); ++ z) { ^