Compilare: user.cpp: In function ‘void read()’: user.cpp:18:28: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i=0; i<a.size(); cin >> a[i++]); ^ user.cpp: At global scope: user.cpp:21:6: warning: ISO C++ forbids declaration of ‘main’ with no type [-Wreturn-type] main() ^ user.cpp: In function ‘int main()’: user.cpp:33:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (x<a.size() && x>=0 && a[x]==y) cout << x << '\n'; ^