Dialog Field Validation

In Report this if for to check the null values.
boolean getFromDialog()
{
boolean ret;
;
_CustAccount = dlgField.value();

if(_CustAccount == "")
{
checkfailed("Enter the value");
}
else
ret = true;

return ret;
}
______
This is to validate based on the condition.
boolean getFromDialog()
{
boolean ret;
;
_CustAccount = dlgField.value();

if(_CustAccount >= "4000" && _CustAccount <="4010")
{
ret = true;
}
else
checkfailed("Enter the values bet ween 4000 to 4010");

return ret;
}