/in/foo.cc:4:7: error: 'maxn' was not declared in this scope
 int a[maxn];
       ^~~~
/in/foo.cc: In function 'bool Bsearch(int, int, int)':
/in/foo.cc:9:6: error: 'a' was not declared in this scope
  if (a[m] == x) return true;
      ^
/in/foo.cc: In function 'int main()':
/in/foo.cc:20:8: error: 'a' was not declared in this scope
   cin>>a[i];
        ^
/in/foo.cc:24:20: error: 'a' was not declared in this scope
    if (Bsearch(1,n,a[i]+a[j])) ans++;
                    ^
/in/foo.cc: In function 'bool Bsearch(int, int, int)':
/in/foo.cc:12:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^