static void Main(string[] args)
{
Console.WriteLine("***** Fun with Nullable Data *****\n");
DatabaseReader dr = new DatabaseReader();
// Get int from "database".
int? i = dr.GetIntFromDatabase();
if (i.HasValue)
{
Console.WriteLine("Value of i is {0}", i.Value);
}
else
Console.WriteLine("Value of 'i' is undefined");
// Get bool from "database".
bool? b = dr.GetBoolFromDatabase();
if (b !=null)
{
Console.WriteLine("Value of 'b' is: {0}", b.Value);
}
else
Console.WriteLine("Value of 'b' is undefined");
// If the value from GetIntFromDatabase() is null,
// assisgn local variable to 100
int myData = dr.GetIntFromDatabase() ?? 100;
Console.WriteLine("Value of myData: {0}", myData);
Console.ReadKey();
}
static void Main(string[] args)
{
Console.WriteLine("***** Fun with nullable data *****\n");
DatabaseReader dr = new DatabaseReader();
//get int from "database"
int? i = dr.GetIntFromDatabase();
if (i.HasValue)
Console.WriteLine("Value of 'i' is: {0}", i.Value);
else
Console.WriteLine("Value of 'i' is undefined.");
//get bool from "Database"
bool? b = dr.GetBoolFromDatabase();
if (b != null)
Console.WriteLine("Value of 'b' is: {0}", b.Value);
else
Console.WriteLine("Value of 'b' is undefined.");
int myData = dr.GetIntFromDatabase() ?? 100;//could also be done long-
//hand via an if/else statement.
Console.WriteLine("Value of myData: {0}", myData);
TesterMethod(null);
Console.ReadLine();
}
static void Main(string[] args)
{
// Uncomment to generate compiler errors.
// bool myBool = null;
// int myInt = null;
Console.WriteLine("***** Fun with Nullable Data *****\n");
DatabaseReader dr = new DatabaseReader();
// Get int from 'database'.
int?i = dr.GetIntFromDatabase();
if (i.HasValue)
{
Console.WriteLine("Value of 'i' is: {0}", i);
}
else
{
Console.WriteLine("Value of 'i' is undefined.");
}
// Get bool from 'database'.
bool?b = dr.GetBoolFromDatabase();
if (b != null)
{
Console.WriteLine("Value of 'b' is: {0}", b);
}
else
{
Console.WriteLine("Value of 'b' is undefined.");
}
// If the value from GetIntFromDatabase() is null,
// assign local variable to 100.
int?myData = dr.GetIntFromDatabase() ?? 100;
Console.WriteLine("Value of myData: {0}", myData);
Console.ReadLine();
}
static void Main(string[] args)
{
Console.WriteLine("***** Fun with nullable data *****\n");
DatabaseReader dr = new DatabaseReader();
int? i = dr.GetIntFromDatabase();
if(i.HasValue)
Console.WriteLine("Value of i is: {0}", i.Value);
else
Console.WriteLine("Value of i is undefined.");
bool? b = dr.GetBoolFromDatabase();
if(b != null)
Console.WriteLine("Value of b is: {0}", b.Value);
else
Console.WriteLine("Value of b is undefined.");
int myData = dr.GetIntFromDatabase() ?? 100;
Console.WriteLine("Value of myData is: {0}", myData);
Console.ReadLine();
}
static void Main(string[] args)
{
Console.WriteLine("***** Fun with Nullable Data *****\n");
DatabaseReader dr = new DatabaseReader();
//从"数据库"获取int
int?i = dr.GetIntFromDatabase();
if (i.HasValue)
{
Console.WriteLine("Value of 'i' is:{0}", i.Value);
}
else
{
Console.WriteLine("Value of 'i' is undefined");
}
//从"数据库"获取bool
bool?b = dr.GetBoolFromDatabase();
if (b != null)
{
Console.WriteLine("Value of 'b' is :{0}", b.Value);
}
else
{
Console.WriteLine("Value of 'b' is undefined");
}
Console.WriteLine();
//从GetIntFromDatabase()返回的值为null时,将局部变量赋值为100
int myData = dr.GetIntFromDatabase() ?? 100;
Console.WriteLine("Value of myData:{0}", myData);
Console.ReadLine();
}
static void Main(string[] args)
{
//bool myBool = null; ERROR: non-nullable value type
string myString = null; //OK, Strings are reference types
LacalNullableVariables();
DatabaseReader dr = new DatabaseReader();
int? i = dr.GetIntFromDatabase();
if (i.HasValue)
{
Console.WriteLine("Value of i is: {0}", i.Value);
}
else
{
Console.WriteLine("Value of i is undefined");
}
bool? b = dr.GetBoolFromDatabase();
if (b == null) {
Console.WriteLine("b in undefined");
}
else
{
Console.WriteLine("Value of b is: {0}", b.Value);
}
int myData = dr.GetIntFromDatabase() ?? 100;
Console.WriteLine("Value of myData: {0}", myData);
Console.ReadLine();
}
static void Main(string[] args)
{
Console.WriteLine("***** Fun with Nullable Data *****\n");
DatabaseReader dr = new DatabaseReader();
int?i = dr.GetIntFromDatabase();
if (i.HasValue)
{
Console.WriteLine("Value of 'i' is {0}", i.Value);
}
else
{
Console.WriteLine("Value of 'i' is undefined.");
}
bool?b = dr.GetBoolFromDatabase();
if (b != null)
{
Console.WriteLine("Value of 'b' is {0}", b.Value);
}
else
{
Console.WriteLine("Value of 'b' is undefined.");
}
// If the value from GetIntFromDatabase() is null,
// assign local variable to 100.
int myData = dr.GetIntFromDatabase() ?? 100;
Console.WriteLine("Value of myData: {0}", myData);
Console.ReadLine();
}
static void Main(string[] args)
{
// Compiler errors!
// Value types cannot be set to null!
//bool myBool = null;
//int myInt = null;
// OK! Strings are reference types.
string myString = null;
Console.WriteLine("***** Fun with Nullable Data *****\n");
DatabaseReader dr = new DatabaseReader();
// Get int from "database".
int?i = dr.GetIntFromDatabase();
if (i.HasValue)
{
Console.WriteLine("Value of 'i' is: {0}", i.Value);
}
else
{
Console.WriteLine("Value of 'i' is undefined.");
}
// Get bool from "database".
bool?b = dr.GetBoolFromDatabase();
if (b != null)
{
Console.WriteLine("Value of 'b' is: {0}", b.Value);
}
else
{
Console.WriteLine("Value of 'b' is undefined.");
}
// If the value from GetIntFromDatabase() is null,
// assign local variable to 100.
int myData = dr.GetIntFromDatabase() ?? 100;
Console.WriteLine("Value of myData: {0}", myData);
// Long-hand notation not using ?? syntax.
int?moreData = dr.GetIntFromDatabase();
if (!moreData.HasValue)
{
moreData = 100;
}
Console.WriteLine("Value of moreData: {0}", moreData);
Console.WriteLine($"I'm passing null:\n");
TesterMethod(null);
Console.WriteLine($"I'm passing null:\n");
TesterMethodByUsingNullConditionalOperator(null);
Console.WriteLine($"I'm passing null:\n");
TesterMethodByUsingNullConditionalAndNullCoalescingOperator(null);
Console.ReadLine();
}
