/in/foo.cc: In function 'int main()':
/in/foo.cc:61:9: warning: unused variable 'a' [-Wunused-variable]
     int a[10], Tot;
         ^
/in/foo.cc:61:16: warning: unused variable 'Tot' [-Wunused-variable]
     int a[10], Tot;
                ^~~
/in/foo.cc: In function 'void prime_table()':
/in/foo.cc:14:20: warning: iteration 1003 invokes undefined behavior [-Waggressive-loop-optimizations]
       if(!isprime[i]) prime[++tot] = i;
           ~~~~~~~~~^
/in/foo.cc:13:22: note: within this loop
     for(int i = 2; i <= maxn; ++i) {
                    ~~^~~~~~~