对以下声明做下面的事情：如果该声明不是一个定义，请为它写一个

char ch;
string s;
int count = 1;
const double pi = 3.1415926535897932385;
extern int error_number;
const char* name = "Njat";
const char* season[] = { "spring","summer","fall","winter" }
struct Date{ int d,m,y; };
int day(Date* p) { return p->d; }
double sqrt(double);
template<class T>T abs(T a) { return a<0 ? -a:a; }
typedef complex<short> Point;
struct User;
enum Beer{ Carlsberg,Tuborg,Thor };
namespace NS { int a; }