Class vector has no member - c++

Question

I'm collecting names and test scores to populate a vector. Both the function and main method can't recognize the struct's members. How can I get it to see the members? Or is there a better way to populate a vector of structs with user input using a function?
I've searched other similar posts, but it seems like it's just a simple code error I missed.
#include <iostream>
#include <vector>
using namespace std;
const int classSize = 1;
struct StudentType {
string studentFName;
string studentLName;
int testScore;
char grade;
};
vector<StudentType> collectStudentData(vector<StudentType> students[classSize]) {
for (int i = 0; i < classSize; i++) {
cout << "Student " << i << "'s name and test score" << endl;
cin >> students[i].studentFName >> students[i].studentLName >> students[i].testScore;
}
return students[classSize];
};
int main() {
vector<StudentType> students[classSize] = {};
students[classSize] = collectStudentData(students);
cout << students[1].studentFName << students[1].studentLName << students[1].studentFName;
};
'studentFName': is not a member of 'std::vector>'

Answer 1

This line creates an array of vectors:
vector<StudentType> students[classSize] = {};
What you want is this a single vector:
vector<StudentType> students;
Where that gets initialized to a zero-length array.
When it comes to adding data you don't need to return from the other method, you can pass in a reference and add to it:
void collectStudentData(vector<StudentType>& students) {
for (int i = 0; i < classSize; i++) {
// Read in one at a time
StudentType student;
cout << "Student " << i << "'s name and test score" << endl;
cin >> student.studentFName >> student.studentLName >> student.testScore;
// Add to the array
students.push_back(student);
}
}
Ideally classSize is either passed in as an argument, or you just type a blank line to end input. Using a global variable is really messy and should be strongly discouraged.

Answer 2

vector<StudentType> students[classSize]
Is one issue. You are not declaring a function that takes a vector, you are declaring a function that takes an array of vectors.
Secondly, if you only applied that change you would be passing an empty vector, you can initialize vector to be a particular size by passing in the size to the constructor.
Furthermore, it seems that you would benefit from passing the students vector by reference
vector<StudentType>& students
instead, the & creates a reference. Right now your code is copying the vector when it is passed into the function
#include <iostream>
#include <vector>
using namespace std;
const int classSize = 1;
struct StudentType {
string studentFName;
string studentLName;
int testScore;
char grade;
};
void collectStudentData(vector<StudentType>& students) {
for (int i = 0; i < classSize; i++) {
cout << "Student " << i << "'s name and test score" << endl;
cin >> students[i].studentFName >> students[i].studentLName >> students[i].testScore;
}
return students;
};
int main() {
vector<StudentType> students{classSize};
collectStudentData(students);
cout << students[0].studentFName << students[0].studentLName << students[0].studentFName;
};
If you wanted to improve the code further, you would use an iterator in the for loop instead, and preferably you wouldn't need to construct the vector in main, and pass it into a function to mutate it. You could just construct it and return it from the function.