View Compilation Error

0_0_3071733_21560.cpp: In function `void gao(int)':
0_0_3071733_21560.cpp:6: error: `$_' undeclared (first use this function)
0_0_3071733_21560.cpp:6: error: (Each undeclared identifier is reported only once for each function it appears in.)
0_0_3071733_21560.cpp: In function `int main()':
0_0_3071733_21560.cpp:29: error: `$_' undeclared (first use this function)