Compilare: main.cpp: In function 'void convex_hull()': main.cpp:136:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < pts.size(); ++i){ ~~^~~~~~~~~~~~ main.cpp: In function 'double area()': main.cpp:151:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 1; i < shanp.size(); ++i){ ~~^~~~~~~~~~~~~~