Compilare: In file included from /usr/include/c++/4.8/cassert:43:0, from user.cpp:10: user.cpp: In function ‘std::string flip(const string&, const int&, const int&)’: user.cpp:18:45: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] assert(0 <= l && l <= r && r < str.size()); ^ user.cpp: In function ‘int to_int(const string&)’: user.cpp:27:34: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < str.size(); ++ i) ^ user.cpp: In function ‘void backtr(std::string, const int&)’: user.cpp:40:38: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int l = 0; l < current.size(); ++ l) ^ user.cpp:41:42: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int r = l; r < current.size(); ++ r) ^ user.cpp: In function ‘int generate_factorful_number()’: user.cpp:1011:37: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < primes.size() && 1LL * ans * primes[i] <= 1000000007; ++ i) { ^ user.cpp: In function ‘void generate_test1()’: user.cpp:362:43: warning: ignoring return value of ‘int system(const char*)’, declared with attribute warn_unused_result [-Wunused-result] system("ping localhost -n 2 >nul"); ^ user.cpp: In function ‘void generate_test2()’: user.cpp:399:43: warning: ignoring return value of ‘int system(const char*)’, declared with attribute warn_unused_result [-Wunused-result] system("ping localhost -n 2 >nul"); ^ user.cpp: In function ‘void generate_test3()’: user.cpp:442:43: warning: ignoring return value of ‘int system(const char*)’, declared with attribute warn_unused_result [-Wunused-result] system("ping localhost -n 2 >nul"); ^ user.cpp: In function ‘void generate_test4()’: user.cpp:485:43: warning: ignoring return value of ‘int system(const char*)’, declared with attribute warn_unused_result [-Wunused-result] system("ping localhost -n 2 >nul"); ^ user.cpp: In function ‘void generate_test5()’: user.cpp:528:43: warning: ignoring return value of ‘int system(const char*)’, declared with attribute warn_unused_result [-Wunused-result] system("ping localhost -n 2 >nul"); ^ user.cpp: In function ‘void generate_test6()’: user.cpp:576:43: warning: ignoring return value of ‘int system(const char*)’, declared with attribute warn_unused_result [-Wunused-result] system("ping localhost -n 2 >nul"); ^ user.cpp: In function ‘void generate_test7()’: user.cpp:620:43: warning: ignoring return value of ‘int system(const char*)’, declared with attribute warn_unused_result [-Wunused-result] system("ping localhost -n 2 >nul"); ^ user.cpp: In function ‘void generate_test8()’: