> usingnamespace std;
First of all, you need to stop using whatever crappy code colouring tool which removed the space between "using" and "namespace".

It's hard enough to help people sometimes without having extra problems inserted.

> i get the "fatal error" that says unresolved external symbol

You've got this
int seqSearch(int list[], int listLength, int searchItem);

But you also need to write the function itself