How to Check Null Value in C#?

[sivaranjan]

Hi Folks,
I am recently started doing the C# programming language. Before starting this I have done C and C++ (basic programs). I have told to create a small program in which I have to check the null value. I have tried lot of different things but was not successful. So its sincere request to tell me how to Check Null Value in C#..?? If you provide the coding for the same, that would be much grateful. Hoping that someone would help me soon..!!

[Viensterrr]

I think that before looking at the code you should understand the basic concepts about the null value, since you are new to C#. You can use the null value in a relational database is used when the value in a column is unknown or missing. Also don't go on the name of the function. A null is neither an empty string nor a zero value for data types and numeric data types respectively. Also for your knowledge I would like to tell you that the System.Data.SqlTypes namespace provides null semantics by implementing the INullable interface.

[Solitario]

The coding of the null value is very much similar to the coding that I have provided. So just have a look at the coding which can make you to understand more properly. Here is the coding for that :

if(dr["AdmissionDate"] == DBNull.Value)
{
//Null value in AdmissionDate Column
}
else
{
//Not Null
}

[kyosang]

The example that I have provided is little bit complicated but you can get an idea about checking the null values in C# programming language. I know the code is bit large but will definitely help you.

static private void WorkWithSqlNulls()
{
    DataTable table = new DataTable();

    DataColumn idColumn =
        table.Columns.Add("Roll", typeof(SqlInt32));
    DataColumn descColumn =
        table.Columns.Add("Information", typeof(SqlString));

    DataRow nRow = table.NewRow();
    nRow["Roll"] = 123;
    nRow["Information"] = "Side Mirror";
    table.Rows.Add(nRow);

    nRow = table.NewRow();
    nRow["Roll"] = SqlInt32.Null;
    nRow["Information"] = SqlString.Null;
    table.Rows.Add(nRow);

    SqlBoolean isColumnNull = false;
    SqlInt32 rollValue = SqlInt32.Zero;
    SqlString informationValue = SqlString.Null;

    foreach (DataRow row in table.Rows)
    {
        rollValue = (SqlInt32)row["Roll"];
        informationValue = (SqlString)row["Information"];

        isColumnNull = rollValue.IsNull;

        Console.Write("isColumnNull={0}, Roll={1}, Information={2}",
            isColumnNull, rollValue, informationValue);
        Console.WriteLine();
    }

If you use the above code, it will generate a DataTable with two columns defined as SqlInt32 and SqlString. The code adds one row of known values, one row of null values and then iterates through the DataTable, assigning the values to variables and displaying the output in the console window.

[Zecho]

Follow the steps for checking the null values in C# :

1. As usual you will have to create the variable first . A variable must be declared before using it. You can use the following code for creating the variable :
   

   string myNullVar = null;

2. Then you will have to check that whether the variable is null or not. You can use the following code for that purpose :
   

   if(myNullVar == null) {
   myNullVar = "purple";
   }

3. Afterward you will have to check if the variable is not null. In some cases, you may wan to reassign the variable back to null. The following code is useful for that :
   

   if(myNullVar != null) {
   myNullVar = null;
   }