Select

Syntax:

    Select Case var

    Case value1
      code1

    Case value2
      code2

    Case value_3 To _value4
      code3

    Case Else
      code4

    End Select

Command Availability:

Available on all microcontrollers.

Explanation:

The Select Case control structure is used to select and run a particular section of code, based on the value of var. If var equals value1 then code1 will be run. Once code1 has run, the chip will jump to the End Select command and continue running the program. If none of the other conditions are true, then the code under the Case Else section will be run.

Case var TO var is a range of values. If the value is within the range the code section will be executed.

Case value1, value2, …​ is a list of values, separated by commas. If var equals any of the listed values, that Case’s code section is run. Values can be numbers, characters, or strings; a single Case may list at most 64 values (see Constraints and Error Messages). 

    Select Case Temp
      Case 0, 1, 2
        Print "Low"
      Case 3, 4, 5
        Print "Medium"
      Case Else
        Print "High"
    End Select

Key line: Case 0, 1, 2 — runs Print "Low" if Temp is 0, 1, or 2; only one of the three values needs to match.

Case Else is optional, and the program will function correctly without it.

If there is only one line of code after the Case, the code may look neater if the line is placed after the Case. This is shown below in the example, for cases 3, 4 and 5.

It is important to note that only one section of code will be run when using Select Case.

Example:

    'Program to read a value from a potentiometer, and display a
    'different word based on the result

      #chip 16F877a, 4

    'LCD connection settings
    #define LCD_IO 4
    #define LCD_WIDTH 20                ;specified lcd width for clarity only.  20 is the default width
    #define LCD_DB4 PORTD.4
    #define LCD_DB5 PORTD.5
    #define LCD_DB6 PORTD.6
    #define LCD_DB7 PORTD.7
    #define LCD_RS PORTD.0
    #define LCD_NO_RW
    #define LCD_ENABLE PORTD.2

    DIR PORTA.0 IN
    Do
      Temp = ReadAD(AN0) / 20
      CLS
      Select Case Temp          ' <<< the Select Case this page documents
        Case 0
          Print "None!"
        Case 1
          Print "One"
        Case 2
          Print "Two"
        Case 3: Print "Three"
        Case 4: Print "Four"
        Case 5: Print "Five"
        Case Else
          Print "A lot!"
      End Select
      Wait 250 ms
    Loop

Key line: Select Case Temp — only the single Case branch matching Temp runs, then execution continues after End Select.

See Also:

  • If — two-way branch alternative for simpler conditions
  • Conditions — background on how conditions are evaluated
  • ReadAD — reading the potentiometer value tested in Example 1
  • CLS — clearing the LCD before printing a result, as used in Example 1
  • Print — displaying the selected branch’s text, as used in Example 1
  • Constraints and Error Messages — the 64-value Case list limit, and other compiler constraints
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