Checkboxes

The HTML markup for a checkbox logical input looks very similar to that for radio buttons. The only structural difference is the use of TYPE="checkbox" . Multiple selections are allowed however:

What operating systems have you used?
Macintosh
DOS
Windows
Windows95
OS/2
UNIX

The HTML to produce the above is:

<P>
What operating systems have you used?<BR>
<INPUT type="checkbox" name="os_used" value="mac">Macintosh<BR>
<INPUT type="checkbox" name="os_used" value="dos">DOS<BR>
<INPUT type="checkbox" name="os_used" value="win">Windows<BR>
<INPUT type="checkbox" name="os_used" value="win95">Windows95<BR>
<INPUT type="checkbox" name="os_used" value="os2">OS/2<BR>
<INPUT type="checkbox" name="os_used" value="unix">UNIX<BR>
</P>

how do multiple responses get transmitted if there's only one value allowed for a given name?

Let's assume that the user checks the boxes for Macintosh, DOS, and Windows95.

• The value of os_used would be

   mac|dos|win95
  

  , where the

   |
  

  represents a separator (usually a null character).
• There is one value for the NAME defined as os_used, but it contains all of the options which the user selected.
• The CGI program will need to be able to take the value and split it up into its components.
• Fortunately, most CGI languages have libraries which were written to accept form-entered data, so this should not be a problem.
• More on this later.