C++ beginners question how to access variables - c++

Question

So basicly my questions include when to use parameters and when I dont need them.
I try to learn from examples and this one I can't fully understand:
I will add the questions to the part where I dont understand something after "//" on the right side of the line.
Maybe someone can give me a good explanation, what I need to do in which scenario or good sources where I can look this up on my own.
class Student with public attributes:
#include <iostream>
class Student
{
public:
int stud_ID;
char stud_Name[22];
int stud_Age;
};
function which I want included in int main():
void studentinformation(Student); //#1Why do I must include (Student) in this fuction? ->
// If I dont add this parameter in here, there is no connection ->
//to the function studentinformation(s) in int main.
//Why exactly is that the case ?
main function to get information:
int main(){
Student s;
std::cout<<"Type in ID:";
std::cin >> s.stud_ID;
std::cout<<"Type in youre Name:";
std::cin.ignore(); //
std::cin.getline(s.stud_Name, 22); //#2 Why is std::getline(std::cin, s.stud_Name) not working ?->
std::cout<<"Type in age:"; //#3 Or is there a better alternative ?
std::cin >> s.stud_Age;
studentinformation(s); //#4 Why do I must include the parameter s ?
return 0;
}
function to print information:
void studentinformation(Student s) // #5 Why do I must include the Parameters ?
{ std::cout<<" Student information:"<< std::endl;
std::cout<<" Student ID:" << s.stud_ID << std::endl;
std::cout<<" Name:" << s.stud_Name<< std::endl;
std::cout<<" Age:" << s.stud_Age<< std::endl;
}

Answer 1

studentinformation() is a free function with no connection to any instance of Student which is why you need to supply one as an argument.
std::getline() works on std::strings ...
... and you'd be doing yourself a favour if you changed char stud_Name[22]; to std::string stud_Name;.
For the same reason as in 1.
For the same reason as in 1. 1, 4 and 5 are questioning the same thing.
An alternative would be to make studentinformation() a Student member function instead. You could then call s.studentinformation(); to print info about that particular student.
class Student {
public:
int stud_ID;
std::string stud_Name; // suggested change
int stud_Age;
void studentinformation() const { // const since the object (this) won't be altered
std::cout << " Student information:" << '\n';
std::cout << " Student ID:" << stud_ID << '\n';
std::cout << " Name:" << stud_Name << '\n';
std::cout << " Age:" << stud_Age << '\n';
}
};