I'm getting error in q no 3 of class assignment

the error is as follows →
main.cpp:26:11: error: ‘s’ was not declared in this scope
26 | max = s[0];
| ^
main.cpp:38:64: error: ‘i’ was not declared in this scope
38 | cout << "the highest mark is " << max << " of student " << i + 1;
| ^
main.cpp: In function ‘int main()’:
main.cpp:54:5: error: expected primary-expression before ‘]’ token
54 | s[].highest_mark ();
| ^

Whereas the code is as follows →
#include
#include
#include <string.h>
using namespace std;
//class student and store the marks and print highest
class student
{

int mark;
public:
void getdata ()
{
cin >> mark;
}
void highest_mark ()
{
int max;
max = s[0];
for (int i = 0; i < 5; i++)
{
if (max > s[i])
{
max = max;
}
else
{
max = s[i];
}
}
cout << "the highest mark is " << max << " of student " << i + 1;
}

};

int
main ()
{

student s[5];
for (int i = 0; i < 5; i++)
{
cout << "Enter mark for " << i + 1 << " student : ";
s[i].getdata ();
}
cout << endl;
s[].highest_mark ();

return 0;
}