LNK2019 无法解析的外部符号 小白求助哪里错了怎么修改啊

#include
using namespace std;
#include
struct stringy {
char * kk;
int ct;
};
int set(stringy &f, const char* str);
void show(const stringy &f, int n = 1);
void show(char* qq, int n = 1);
int main()
{
stringy beany;
char testing[] = "Reality isn't what it used to be.";
set(beany, testing);
show(beany);
show(beany, 2);
testing[0] = 'D';
testing[1] = 'u';
show(testing);
show(testing, 3);
show("Done!");
system("pause");
return 0;
}
int set(stringy &f, const char* str)
{
int count = 0;
for (int i = 0; str[i] != '\0'; i++)
{
f.kk[i] = str[i];
count = i + 1;
}
return count;

}

void show(const stringy &f, int n)
{
for (int i = 0; i<n; i++)
cout << f.kk << endl;

}
void show(const char* qq, int n)
{
for (int i = 0; i<n; i++)
cout << qq << endl;
}

show("Done!");
c++里这么写,done是string

const char * s = "done";
show(s);