triunghi5.cpp: In function 'std::vector<point, std::allocator<point> > convex_hull(std::vector<point, std::allocator<point> >&)': triunghi5.cpp:45: warning: comparison between signed and unsigned integer expressions triunghi5.cpp:49: warning: comparison between signed and unsigned integer expressions triunghi5.cpp: In function 'double determine_maximum_area(int)': triunghi5.cpp:87: warning: comparison between signed and unsigned integer expressions triunghi5.cpp: In function 'int main()': triunghi5.cpp:97: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result triunghi5.cpp:98: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result triunghi5.cpp:100: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result triunghi5.cpp:102: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result triunghi5.cpp: In function 'bool cmp(point, point)': triunghi5.cpp:19: warning: control reaches end of non-void function