Compilare: user.cpp: In function ‘void read()’: user.cpp:16:28: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i=0; i<a.size(); i++) ^ user.cpp:19:35: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int j=0; j<a[i].size(); j++) ^ user.cpp: In function ‘void solve()’: user.cpp:47:39: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i=1+c; i<a[c].size()-c; i++) ^ user.cpp:52:36: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i=1+c; i<a.size()-c; i++) ^ user.cpp: At global scope: user.cpp:75:6: warning: ISO C++ forbids declaration of ‘main’ with no type [-Wreturn-type] main() ^ user.cpp: In function ‘void solve()’: user.cpp:72:13: warning: ‘x’ may be used uninitialized in this function [-Wmaybe-uninitialized] write(x); ^