foo.cc: In function 'int main()':
foo.cc:36:18: warning: suggest parentheses around comparison in operand of '&' [-Wparentheses]
   36 |         if (n & 1==1)
      |                 ~^~~
foo.cc:72:25: warning: 'dd' may be used uninitialized in this function [-Wmaybe-uninitialized]
   72 |                         if (abs(n/2-j)<dd) {num=j;dd=abs(n/2-j);}
      |                         ^~
foo.cc:76:39: warning: 'num' may be used uninitialized in this function [-Wmaybe-uninitialized]
   76 |             second=change(second,a[num+1]);
      |                                    ~~~^~

[Hydro](https://hydro.ac)提供评测服务