Compilare: user.cpp: In function ‘int main()’: user.cpp:32:36: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (pairs.size() > last) { ^ user.cpp:49:40: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < pairs.size(); i++, c = 1 - c) ^ user.cpp:46:13: warning: unused variable ‘hLen’ [-Wunused-variable] int hLen = len / 2; ^ user.cpp:9:39: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("brackets.in", "r", stdin); ^ user.cpp:10:41: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("brackets.out", "w", stdout); ^ user.cpp:13:20: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d", &T); ^ user.cpp:16:26: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d\n", &n); ^ user.cpp:18:20: warning: ignoring return value of ‘char* gets(char*)’, declared with attribute warn_unused_result [-Wunused-result] gets(s + 1); ^ /tmp/ccjd4Hzl.o: In function `main': user.cpp:(.text.startup+0xa7): warning: the `gets' function is dangerous and should not be used.