Compilare: main.cpp: In member function 'BigInt BigInt::add(BigInt)': main.cpp:37:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < c.digits.size(); i++) ~~^~~~~~~~~~~~~~~~~ main.cpp:39:9: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if(i < digits.size()) ~~^~~~~~~~~~~~~~~ main.cpp:42:9: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if(i < a.digits.size()) ~~^~~~~~~~~~~~~~~~~ main.cpp: In member function 'BigInt BigInt::multiplies(BigInt)': main.cpp:66:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < digits.size(); i++) ~~^~~~~~~~~~~~~~~ main.cpp:67:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int j = 0; j < a.digits.size(); j++) ~~^~~~~~~~~~~~~~~~~ main.cpp:70:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < c.digits.size() - 1; i++) ~~^~~~~~~~~~~~~~~~~~~~~ main.cpp: At global scope: main.cpp:113:6: warning: ISO C++ forbids declaration of 'main' with no type [-Wreturn-type] main() ^