Although seem lie, in the C# language not exist a dialog box for ask a data. If you don’t want create your own dialog box and don’t need personalize it, you can use the sentence Inputbox that you can find in Microsoft.VisualBasic assembly.
This sentence show a modal dialog with a label, text box, a button accept and other button for cancel.

The definition of sentence InputBox is as follow:

       
public static string InputBox(
        string Prompt,
string Title,
string DefaultResponse,
int XPos,
int YPos)

• Prompt: Dialog message
• Title: Optional. Dialog title.
• DefaultResponse: Optional. answer by default.
• xPos: Optional. Coordinate X, centered by default.
• yPos: Optional. Coordinate Y, centered by default.

Steps for insert an InputBox in C#:

1. Insert a reference to Microsoft.VisualBasic assembly:

2. Insert the sentence:

private void btnClickInputBox_Click(object sender, EventArgs e)
{
    string texto = Microsoft.VisualBasic.Interaction.InputBox(
        "Texto de la pregunta",
        "Titulo del diálogo",
        "Respuesta por defecto");
}

Note: if the user cancels the dialog then the statement returns an empty string

Result: