Can't find the error (related to % ?)

[gameprogrammer]

  int a[21],i;
  a[0]=0; a[1]=1;
  for (i=2;i<=20;i++)
      a[i]=(7*a[i-1])%1000-(10*a[i-2])%1000+(pow(3,i))%1000;

[Peter87]

% can only be used on integers but pow returns a double.

[gameprogrammer]

Thanks, changing it to int(pow(3,i)) gets rid of the problem.