View Compilation Error

0_0_35841908_24607.cpp:4:28: error: expected unqualified-id before 'double'
 const double PI=acos(-1.0),double g=9.8;
                            ^
0_0_35841908_24607.cpp: In function 'int check(double)':
0_0_35841908_24607.cpp:13:26: error: 'g' was not declared in this scope
         double Vy=sqrt(2*g*H+Vy0*Vy0); //竖直方向动能定理 
                          ^