Step 1: Start Visual Studio and create Windows Form Application in C# or VB as you wish.
Step 2: Add CheckBox and RichTextBox to your form.
Step 3: Add KeyPress and KeyDown events to RichTextBox.
Step 4: Now add the following code defined in KeyPress and KeyDown event into your code.

How it Works

It's simple, just identify which key is pressed in richTextBox, if it is ( open round bracket then read SelectionStart from richTextBox and insert opposite character to richTextBox at position SelectionStart+1.
Finally add one line once opposite character is inserted and that is e.Handled=true;

C# Code for Auto Complete Brackets,
  1. using System;
  2. using System.Collections.Generic;
  3. using System.ComponentModel;
  4. using System.Data;
  5. using System.Drawing;
  6. using System.Windows.Forms;
  8. namespace Auto_Complete_Brackets
  9. {
  10. public partial class Form1 : Form
  11. {
  12. public Form1()
  13. {
  14. InitializeComponent();
  15. }
  17. //declare isCurslyBracesKeyPressed variable as Boolean and assign false value
  18. //to check { key is pressed or not
  19. public static Boolean isCurslyBracesKeyPressed = false;
  21. //richTextBox1 KeyPress events
  23. // if key (,{,<,",',[ is pressed then insert opposite key to richTextBox1 at Position SelectionStart+1
  24. // add one line after inserting, e.Handled=true;
  25. //finally set SelectionStart to specified position
  27. private void richTextBox1_KeyPress(object sender, KeyPressEventArgs e)
  28. {
  29. String s = e.KeyChar.ToString();
  30. int sel = richTextBox1.SelectionStart;
  31. if (checkBox1.Checked == true)
  32. {
  33. switch (s)
  34. {
  35. case "(": richTextBox1.Text = richTextBox1.Text.Insert(sel, "()");
  36. e.Handled = true;
  37. richTextBox1.SelectionStart = sel + 1;
  38. break;
  40. case "{":
  41. String t = "{}";
  42. richTextBox1.Text = richTextBox1.Text.Insert(sel, t);
  43. e.Handled = true;
  44. richTextBox1.SelectionStart = sel + t.Length - 1;
  45. isCurslyBracesKeyPressed = true;
  46. break;
  48. case "[": richTextBox1.Text = richTextBox1.Text.Insert(sel, "[]");
  49. e.Handled = true;
  50. richTextBox1.SelectionStart = sel + 1;
  51. break;
  53. case "<": richTextBox1.Text = richTextBox1.Text.Insert(sel, "<>");
  54. e.Handled = true;
  55. richTextBox1.SelectionStart = sel + 1;
  56. break;
  58. case "\"": richTextBox1.Text = richTextBox1.Text.Insert(sel, "\"\"");
  59. e.Handled = true;
  60. richTextBox1.SelectionStart = sel + 1;
  61. break;
  63. case "'": richTextBox1.Text = richTextBox1.Text.Insert(sel, "''");
  64. e.Handled = true;
  65. richTextBox1.SelectionStart = sel + 1;
  66. break;
  67. }
  68. }
  69. }
  72. // richTextBox1 Key Down event
  73. /*
  74. * when key { is pressed and {} is inserted in richTextBox
  75. * and isCurslyBracesKeyPressed is true then insert some blank text to richTextBox1
  76. * when Enter key is down
  77. * it will look like this when Enter key is down
  79. {
  80. |
  81. }
  83. * */
  85. private void richTextBox1_KeyDown(object sender, KeyEventArgs e)
  86. {
  87. int sel = richTextBox1.SelectionStart;
  88. if (e.KeyCode == Keys.Enter)
  89. {
  90. if(isCurslyBracesKeyPressed==true)
  91. {
  92. richTextBox1.Text = richTextBox1.Text.Insert(sel, "\n \n");
  93. e.Handled = true;
  94. richTextBox1.SelectionStart = sel + " ".Length;
  95. isCurslyBracesKeyPressed = false;
  96. }
  97. }
  98. }
  99. }
  100. }
VB.Net Code for Auto Complete Brackets
  1. Imports System
  2. Imports System.Collections.Generic
  3. Imports System.ComponentModel
  4. Imports System.Data
  5. Imports System.Drawing
  6. Imports System.Windows.Forms
  7. Public Class Form1
  9. 'declare isCurslyBracesKeyPressed variable as Boolean and assign false value
  10. 'to check { key is pressed or not
  11. Public Shared isCurslyBracesKeyPressed As [Boolean] = False
  13. 'RichTextBox1 KeyPress events
  15. ' if key (,{,<,",',[ is pressed then insert opposite key to RichTextBox1 at Position SelectionStart+1
  16. ' add one line after inserting, e.Handled=true;
  17. 'finally set SelectionStart to specified position
  19. Private Sub RichTextBox1_KeyPress(sender As Object, e As KeyPressEventArgs) Handles RichTextBox1.KeyPress
  20. Dim s As [String] = e.KeyChar.ToString()
  21. Dim sel As Integer = RichTextBox1.SelectionStart
  22. If checkBox1.Checked = True Then
  23. Select Case s
  24. Case "("
  25. RichTextBox1.Text = RichTextBox1.Text.Insert(sel, "()")
  26. e.Handled = True
  27. RichTextBox1.SelectionStart = sel + 1
  28. Exit Select
  30. Case "{"
  31. Dim t As [String] = "{}"
  32. RichTextBox1.Text = RichTextBox1.Text.Insert(sel, t)
  33. e.Handled = True
  34. RichTextBox1.SelectionStart = sel + t.Length - 1
  35. isCurslyBracesKeyPressed = True
  36. Exit Select
  38. Case "["
  39. RichTextBox1.Text = RichTextBox1.Text.Insert(sel, "[]")
  40. e.Handled = True
  41. RichTextBox1.SelectionStart = sel + 1
  42. Exit Select
  44. Case "<"
  45. RichTextBox1.Text = RichTextBox1.Text.Insert(sel, "<>")
  46. e.Handled = True
  47. RichTextBox1.SelectionStart = sel + 1
  48. Exit Select
  50. Case """"
  51. RichTextBox1.Text = RichTextBox1.Text.Insert(sel, """""")
  52. e.Handled = True
  53. RichTextBox1.SelectionStart = sel + 1
  54. Exit Select
  56. Case "'"
  57. RichTextBox1.Text = RichTextBox1.Text.Insert(sel, "''")
  58. e.Handled = True
  59. RichTextBox1.SelectionStart = sel + 1
  60. Exit Select
  61. End Select
  62. End If
  63. End Sub
  66. ' RichTextBox1 Key Down event
  67. '
  68. ' * when key { is pressed and {} is inserted in richTextBox
  69. ' * and isCurslyBracesKeyPressed is true then insert some blank text to RichTextBox1
  70. ' * when Enter key is down
  71. ' * it will look like this when Enter key is down
  72. '
  73. ' {
  74. ' |
  75. ' }
  76. '
  77. ' *
  79. Private Sub RichTextBox1_KeyDown(sender As Object, e As KeyEventArgs) Handles RichTextBox1.KeyDown
  80. Dim sel As Integer = RichTextBox1.SelectionStart
  81. If e.KeyCode = Keys.Enter Then
  82. If isCurslyBracesKeyPressed = True Then
  83. RichTextBox1.Text = RichTextBox1.Text.Insert(sel, vbLf & " " & vbLf)
  84. e.Handled = True
  85. RichTextBox1.SelectionStart = sel + " ".Length
  86. isCurslyBracesKeyPressed = False
  87. End If
  88. End If
  89. End Sub
  90. End Class