Compilare: user.cpp: In function ‘bool showVector(const std::vector<int>&)’: user.cpp:10:32: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 1; i < a.size(); i++) { ^ user.cpp:14:1: warning: no return statement in function returning non-void [-Wreturn-type] } ^ user.cpp: In function ‘void comb(std::vector<int>&, int, int)’: user.cpp:17:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (k >= a.size()) { ^ user.cpp: At global scope: user.cpp:28:6: warning: ISO C++ forbids declaration of ‘main’ with no type [-Wreturn-type] main() { ^