Compilare: user.cpp: In function ‘void read()’: user.cpp:16:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=1; i<=n; i++) ^ user.cpp:19:24: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=1 ; i<=m; i++) ^ user.cpp: In function ‘bool valid(int, int)’: user.cpp:26:25: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] {if (x<=0 || y<=0 || y>n || x>n) ^ user.cpp:26:32: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] {if (x<=0 || y<=0 || y>n || x>n) ^ user.cpp: In function ‘int lee()’: user.cpp:60:1: warning: control reaches end of non-void function [-Wreturn-type] } ^