Getting an "overloaded member function not found in *"

[aesguitar]

I'm getting an error when I try to build the program. I'm trying to build a small Qt application, but I can't test what I've done so far because it won't compile.

Here is the calculator.cpp file

#include "calculator.h"
#include <QLCDNumber>
#include <QString>

Calculator::Calculator(QWidget *parent) :
    QWidget(parent), ui(new Ui::Calculator)
{
    ans = 0;
    currVal = 0;
    setupUi(this);

}

QString Calculator::getNewVal(qint64 nextDig){

    if(nextDig==0)
    {
        if(currVal > 0)
        {
            QString str = QString::number(currVal);
            str.append("0");
            return str;
        }
        else
        {
            return "0";
        }
    }
    else if(nextDig==1)
    {
        QString str = QString::number(currVal);
        str.append("1");
        return str;
    }
}

void Calculator::on_Zero_clicked()
{
    ui->Display->display(getNewVal(0));
    currVal = ui->Display->intValue();
}

void Calculator::on_One_clicked()
{

}

Here is the main.cpp file

#include "calculator.h"
#include <QApplication>

QString getNewVal(quint64 nextDig);

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    Calculator w;
    w.show();
    
    return a.exec();
}

And here is the calculator.h file

#ifndef CALCULATOR_H
#define CALCULATOR_H

#include "ui_calculator.h"

class Calculator : public QWidget, private Ui::Calculator
{

    Q_OBJECT
    
public:
     Calculator(QWidget *parent = 0);
     long long int ans;
     long long int currVal;
private slots:
    void on_Zero_clicked();
    void on_One_clicked();
private:
    Ui::Calculator *ui;
    QString getNewVal(quint64);


};

#endif // CALCULATOR_H 

Here is the error that the compiler is spitting at me:

"C:\Users\****\Documents\Qt Projects\SimpleCalculator\calculator.cpp:14: error: C2511: 'QString Calculator::getNewVal(qint64)' : overloaded member function not found in 'Calculator'"

I've searched online, but can't figure it out.