/in/foo.cc: In function 'int main()':
/in/foo.cc:21:17: error: 'greater' was not declared in this scope
  sort(a+1,a+n+1,greater<int>()); 
                 ^~~~~~~
/in/foo.cc:21:25: error: expected primary-expression before 'int'
  sort(a+1,a+n+1,greater<int>()); 
                         ^~~
/in/foo.cc:3:13: warning: suggest parentheses around '+' inside '>>' [-Wparentheses]
 #define M (L+R>>1)
            ~^~
/in/foo.cc:25:12: note: in expansion of macro 'M'
   if(check(M))
            ^
/in/foo.cc:3:13: warning: suggest parentheses around '+' inside '>>' [-Wparentheses]
 #define M (L+R>>1)
            ~^~
/in/foo.cc:26:6: note: in expansion of macro 'M'
    L=M;
      ^
/in/foo.cc:3:13: warning: suggest parentheses around '+' inside '>>' [-Wparentheses]
 #define M (L+R>>1)
            ~^~
/in/foo.cc:28:6: note: in expansion of macro 'M'
    R=M-1;
      ^