/in/foo.c:2:27: error: expected ';', ',' or ')' before '&' token
 int max(int x,int k[],int &o){
                           ^
/in/foo.c: In function 'main':
/in/foo.c:25:2: error: variable-sized object may not be initialized
  int c[n]={-1},oo;
  ^~~
/in/foo.c:25:12: warning: excess elements in array initializer
  int c[n]={-1},oo;
            ^
/in/foo.c:25:12: note: (near initialization for 'c')
/in/foo.c:32:14: warning: implicit declaration of function 'max' [-Wimplicit-function-declaration]
   if(i%2)r2+=max(4,&b[0],oo);
              ^~~