undefined reference to outputVLI? : I have to make 2 arrays and use functions to input, output, add, and compare them but I keep getting error message: "undefined reference to outputVLI(int*, int)". I am not sure what this means or how to fix it. Any help would be appreciated

    #include <iostream>
    using namespace std;
    
    const int maxDigits = 100;
    void inputVLI (int vli[], int size);   // Inputs the very long integers
    void outputVLI (int vli[], int size); // Outputs the very long integers
    void addVLI (const int vli1[], const int vli2[], int vli3[], int size1, int size2, int& size3); // Adds the very long integers together
    int compVLI (const int vli1, const int vli2, int size1, int size2); // Compares the very long integers
    
    int main()
    {
        int vli1[maxDigits], vli2[maxDigits], vli3[maxDigits], size1, size2, size3;
        inputVLI (vli1, maxDigits);                                 // Calls the individual functions
        outputVLI (vli1, maxDigits);                                // |
        inputVLI (vli2, maxDigits);                                 // |
        outputVLI (vli2, maxDigits);                                // |
        /*addVLI (vli1, vli2, vli3, size1, size2, size3);           // |
        compVLI (vli1, vli2, size1, size2);*/                       // \/
        return 0;
    }
    
    void inputVLI(int vli[], int size)
    {
        cout << "Enter a very long integer" << endl;
        cin >> vli[maxDigits];
    }
    
    void output (int vli[], int size)
    {
        for (int i=maxDigits; i>=0; i--)
            cout << vli[i];
    }
    
    void addVLI (const int vli1[], const int vli2[], int vli3[], int size1, int size2, int& size3)
    {
    /*
        for (int i=0; i<maxDigits; i++)
        {
            vli3[i]=vli1[i] + vli2[i];
            cout << "The sum of the vli's is:" << vli3[i] << endl;
        }
    */
    }
    
    int compVLI (const int vli1, const int vli2, int size1, int size2)
    {
    /*
        for (int i=0; vli1[maxDigits] && vli2[maxDigits]; i++)
        {
            if (vli1[maxDigits] != vli2[maxDigits])
            {
                return (-1); // -1 is not equal
            }
            return (1); // 1 is equal
        }
    */
    }

