Compilare: user.cpp: In constructor ‘quad_node::quad_node()’: user.cpp:15:21: warning: converting to non-pointer type ‘int’ from NULL [-Wconversion-null] B[0] = B[1] = NULL; ^ user.cpp: In function ‘int main()’: user.cpp:82:42: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen( "imagine.in" , "r", stdin ); ^ user.cpp:83:42: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen( "imagine.out", "w", stdout ); ^ user.cpp:85:26: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf( "%s", S1 + 1 ); ^ user.cpp:90:27: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf( "%c", &ch ); ^