answer.code: In function ‘void FFT(complex*, int, int)’:
answer.code:27:7: warning: ISO C++17 does not allow ‘register’ storage class specifier [-Wregister]
   27 |   For(i,1,len-2)
      |       ^
answer.code:6:37: note: in definition of macro ‘For’
    6 | #define For(i,a,b) for(register int i=a;i<=b;i++)
      |                                     ^
answer.code:38:15: warning: ISO C++17 does not allow ‘register’ storage class specifier [-Wregister]
   38 |           For(j,i,i+(l>>1)-1)
      |               ^
answer.code:6:37: note: in definition of macro ‘For’
    6 | #define For(i,a,b) for(register int i=a;i<=b;i++)
      |                                     ^
answer.code:46:22: warning: ISO C++17 does not allow ‘register’ storage class specifier [-Wregister]
   46 |   if(flag == -1) For(i,0,len-1) f[i].real/=len;
      |                      ^
answer.code:6:37: note: in definition of macro ‘For’
    6 | #define For(i,a,b) for(register int i=a;i<=b;i++)
      |                                     ^
answer.code: In function ‘int main()’:
answer.code:52:24: error: ‘strlen’ was not declared in this scope
   52 |   scanf("%s",s+0),lena=strlen(s+0);
      |                        ^~~~~~
answer.code:4:1: note: ‘strlen’ is defined in header ‘<cstring>’; did you forget to ‘#include <cstring>’?
    3 | #include<cmath>
  +++ |+#include <cstring>
    4 | #define N 5100010
answer.code:53:7: warning: ISO C++17 does not allow ‘register’ storage class specifier [-Wregister]
   53 |   For(i,0,lena-1) a[lena-1-i]=complex(s[i]-'0',0);
      |       ^
answer.code:6:37: note: in definition of macro ‘For’
    6 | #define For(i,a,b) for(register int i=a;i<=b;i++)
      |                                     ^
answer.code:55:7: warning: ISO C++17 does not allow ‘register’ storage class specifier [-Wregister]
   55 |   For(i,0,lenb-1) b[lenb-1-i]=complex(s[i]-'0',0);
      |       ^
answer.code:6:37: note: in definition of macro ‘For’
    6 | #define For(i,a,b) for(register int i=a;i<=b;i++)
      |                                     ^
answer.code:57:7: warning: ISO C++17 does not allow ‘register’ storage class specifier [-Wregister]
   57 |   For(i,0,20) if((1<<i) >= len) {len=1<<i;break;}
      |       ^
answer.code:6:37: note: in definition of macro ‘For’
    6 | #define For(i,a,b) for(register int i=a;i<=b;i++)
      |                                     ^
answer.code:61:7: warning: ISO C++17 does not allow ‘register’ storage class specifier [-Wregister]
   61 |   For(i,0,len-1) a[i]=a[i]*b[i];
      |       ^
answer.code:6:37: note: in definition of macro ‘For’
    6 | #define For(i,a,b) for(register int i=a;i<=b;i++)
      |                                     ^
answer.code:63:7: warning: ISO C++17 does not allow ‘register’ storage class specifier [-Wregister]
   63 |   For(i,0,len-1) ans[i]=int(a[i].real+0.5);
      |       ^
answer.code:6:37: note: in definition of macro ‘For’
    6 | #define For(i,a,b) for(register int i=a;i<=b;i++)
      |                                     ^
answer.code:65:7: warning: ISO C++17 does not allow ‘register’ storage class specifier [-Wregister]
   65 |   For(i,0,len-1) ans[i+1]+=ans[i]/10,ans[i]%=10;
      |       ^
answer.code:6:37: note: in definition of macro ‘For’
    6 | #define For(i,a,b) for(register int i=a;i<=b;i++)
      |                                     ^
answer.code:67:8: warning: ISO C++17 does not allow ‘register’ storage class specifier [-Wregister]
   67 |   Down(i,len,0) putchar(ans[i]+'0');
      |        ^
answer.code:5:38: note: in definition of macro ‘Down’
    5 | #define Down(i,a,b) for(register int i=a;i>=b;i--)
      |                                      ^