simple c question - switch-case

kalleanka · 03-11-2008, 07:24 AM

How do I put multiple optiones as one case?

something like this with comma or semicolon?

switch(aaa){

case a, b:
{
callAfunc();
}
break;
case c :
{
callAfunc();
}
break;

default: callAfunc();

}

Nylex · 03-11-2008, 07:32 AM

You just put the cases underneath each other:

Code:

switch(aaa) {
  case a:
  case b:
    callAfunc();
    break;

  /* Other cases */
}

kalleanka · 03-11-2008, 07:35 AM

ok so if a is the case it calls callAfunc() under case b?

tronayne · 03-11-2008, 07:40 AM

The general form is

Code:

switch (variable) {
case value:
     do something;
     break;
case other value:
     do something else;
     break;
case third value:      /* this value */
case fourth value:     /* or this value */
     do something;
     break;
default:
     break;
}

where "value" is an integer (you can enclose a character [not a string] in single quotes and "something" is a function, arithmetic, or whatever.

Here's an example for processing command line arguments with getopt()

Code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <unistd.h>

#ifndef TRUE
#       define  TRUE    1
#endif
#ifndef FALSE
#       define  FALSE   0
#endif

int     main    (int argc, char *argv [])
{
        int     c;                      /* general-purpose              */
        int     error = FALSE;          /* error flag                   */
        int     vopt = FALSE;           /* verbose option               */
        time_t  t0 = (time_t) 0;        /* start time                   */
        time_t  t1 = (time_t) 0;        /* finish time                  */
        FILE    *in;

        /*      process the command line arguments                      */
        while ((c = getopt (argc, argv, "?v")) != EOF) {
                switch (c) {
                case '?':
                        error = TRUE;
                        break;
                case 'v':
                        vopt = TRUE;
                        break;
                default:
                        (void) fprintf (stderr, "getopt() bug\n");
                        exit (EXIT_FAILURE);
                }
        }
        /*      any errors in the arguments, or a '?' entered...*/
        if (error) {
                (void) fprintf (stderr, "usage: %s [-v] argument...\n",
                    argv [0]);
                exit (EXIT_FAILURE);
        }

kalleanka · 03-11-2008, 07:43 AM

thanks all.

without break it works.

ta0kira · 03-11-2008, 08:18 AM

Yes, although a switch/case blocks appear to be a series of if/else if... blocks, they are really just a single goto statement with a series of labels. That's why the case statements need to have a compiled-in constant.
ta0kira