LateInitializationError: Field '_amount@25125456' has not been initialized

I am trying to do some tax calculation in my flutter project but, It is giving me two errors.

1. LateInitializationError: Field ‘_amount@25125456’ has not been initialized.
2. Error: The operator ‘~/’ isn’t defined for the class ‘String’.
   Try correcting the operator to an existing operator, or defining a ‘~/’ operator.

I am not sure why it is happening can anyone please help me out?

// this is my function

showincomeafterTax() {
if (_amount!.isNotEmpty) {
  taxamount = (_amount * 17 ~/ 100).toString();
  print(taxamount);
} else {
  print('Insert an amount');
}

}

// designing part

 Card(
          shape: RoundedRectangleBorder(
            borderRadius: BorderRadius.circular(15.0),
          ),
          child: Column(
            children: <Widget>[
              Padding(
                padding: EdgeInsets.all(10.0),
              ),
              Container(
                child: Text(
                  'Income after Tax',
                  style: TextStyle(
                    fontWeight: FontWeight.bold,
                  ),
                ),
              ),
              Container(
                child: Column(
                  children: <Widget>[
                    ListTile(
                      leading: Icon(Icons.monetization_on_outlined),
                      title: showincomeafterTax(),
                    ),
                  ],
                ),
              ),
            ],
          ),
        ),

>Solution :

Your error is kinda clear:

Error 1. Your variable _amount has not been initialized. You may declare you variable as

late String _amount;

But you hasn’t assign/initiate it to any value, therefore your program gives the first error.

Error 2. _amount is String type, you cannot use it in a math like a number. I notice that you use operator ~/, which is used in integer. So you need to convert String to a int, example:

if (_amount!.isNotEmpty) {
  int amountDouble = int.parse(_amount);
  taxamount = (amountDouble * 17 ~/ 100).toString();
  print(taxamount);
} else {
  print('Insert an amount');
}