foo.cc: In function 'long long int yueshu(long long int)':
foo.cc:16:10: warning: statement has no effect [-Wunused-value]
     for(i;i<=sqrt(a);i++){              
          ^
foo.cc: At global scope:
foo.cc:28:11: error: '::main' must return 'int'
 void main()
           ^

[Hydro](https://hydro.ac)提供评测服务