char code[10];
Array to hold tag read.
char stephen[11]="8400338A85";
Array to hold known tag.
The arrays aren't even the same size. How can they possibly ever match?
if(code==stephen)
This tests if the address of code and the address of stephen are the same. You know that they are not. Comparing the contents of an array requires a function, like strcmp() for NULL terminated arrays of chars or memcmp() for other arrays.