Compilare: main.cpp: In function 'int main()': main.cpp:64:11: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (nr != x.size() * (x.size() - 1)) { ~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~ main.cpp:6:37: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen("linegraph.in", "r", stdin); ^ main.cpp:7:39: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen("linegraph.out", "w", stdout); ^ main.cpp:15:24: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result] scanf("%d%d", &n, &m); ^ main.cpp:20:25: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result] scanf("%d%d", &x, &y); ^