C# Combobox defined with name my_combobox

private System.Windows.Forms.ComboBox my_combobox;

Define string variable with the text of the combobox item that has to be selected. For example, if the combobox items have text values "item_a" "item_b" "item_c" ... and the item which text is "item_b" has to be selected

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PROGRAMMING HELP | C# | C# COMBOBOX

To get the database connection string from IIS Web.config file using C# code, include System.Configuration directive and then create a string variable to assign the connection string like this:

using System.Configuration;
string connStr = ConfigurationManager.
                  ConnectionStrings["connectionString_Name"].ConnectionString;

If “ConfigurationManager” is not recognized you will need to add reference to: "System.Configuration".See: C# - How to add reference to project

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PROGRAMMING HELP | C# | WEB.CONFIG

To prevent users from entering incorrect data in Windows form application, set restriction to allow only specific characters to be entered in the text box.This example uses KeyPress event to monitor the users input and to apply the restriction required.To avoid code duplication in Windows multiform applications for example, a separate class file is created “CommonFunctions.cs”.
The function to allow only numbers in textbox control is named InputNumbers.
For each Windows form, create a single KeyPress event and call the InputNumbers function inside it.

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PROGRAMMING HELP | C# TEXTBOX KEYPRESS | C#

C# project with two forms

public partial class Form1 : Form // this is the main form

public partial class Form2 : Form // this is the second form

To pass variables (values, data) from Form1 to Form2
Case: public variables in Form2

public string input_variable; // put this in Form2 as global variable

public string output_variable; // put this in Form2 as global variable

in Form1 inside the function that run (call) Form2

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PROGRAMMING HELP | C# FORMS

In order to draw shapes in C# a start point and end point coordinates, and a Pen control must be defined first.
Coordinates in C#The value of x is the location of the point along the x-axis, the 0 is at the extreme left. The value of y is the location of the point along the y-axis, the 0 is at the extreme top.

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PROGRAMMING HELP | C# | C# DRAW SHAPES