Compilare: main.cpp: In function 'void precalculate()': main.cpp:17:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<b.length();i++) ~^~~~~~~~~~~ main.cpp:20:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=1;i<b.length();i++) ~^~~~~~~~~~~ main.cpp:23:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=1;i<a.length();i++) ~^~~~~~~~~~~