Hi. I'm new to C (3 weeks) and I'm attempting an exercise that requires a user to enter in student names along with their grades and store them as structs within a vector. Then this vector is sorted based on the grades. I know C has its own standard algorithms but I wanted to implement an insertion sort myself. Sadly, my code doesn't work. Please help me review. Thanks:

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#include <iostream>
#include <vector>

struct Student
{
    std::string firstName{};
    int grade{};
};

// Insertion Sort
void sortVector(std::vector<Student>& array, int number)
{
    for (int currentIndex{ 1 }; currentIndex < number - 1;   currentIndex)
    {
        int currentValue{ array[currentIndex].grade };
        int previousIndex{ currentIndex - 1 };

        while (previousIndex >= 0 && array[previousIndex].grade > currentValue)
        {
            array.at(previousIndex   1) = array.at(previousIndex);
            --previousIndex;
        }
        array.at(previousIndex   1) = array.at(currentIndex);
    } 

// Print out names and grades
    for (const auto &element : array)
    {
        std::cout << element.firstName << " got a grade of " << element.grade << '\n';
    }
}


int main()
{
    std::cout << "How many students do you want to enter? ";
    int number{};
    std::cin >> number;

    std::vector<Student> array(number);

    for (int i{}; i < number;   i)
    {
        std::cout << "Enter a name: ";
        std::cin >> array[i].firstName;
        std::cout << "Enter a grade: ";
        std::cin >> array[i].grade;
    }

    sortVector(array, number);
}