kimcm@diku.UUCP (Kim Chr. Madsen) (06/20/84)
Jack Jansen: > What does > > switch(i) { > ... > switch(j) { > ... > default: ... > } > } > First of all it doesn't make sense to just put a switch into a switch statement, because when you enter the first switch statement, you just jump to the corresponding case-label and if noone matches then you jump to the default-label, in the outermost switch-level. You can see the default-label in each level as a local label, not known to the switch statements that surrounds the actual switch label. When I say that it doen't make sense to just put a switch statement into another, it's a truth with modifications: a) if it has the form: switch (a) { case 1 : ...; break; case 2 : switch (b) { case 1 : ...; break; default: ...; break; } break; default: ...; break; } it certainly can be usefull as a control statement. b) But if you on the other hand construct a switch- statement like this: switch (a) { switch (b) { : : } } The switch-statements that lies within the outermost switch-statement will never be executed. [sic!] If you want to see it for yourself then try to run this little program: main () { int i = 4,j = 5; switch (i) { switch (j) { case 7 : printf ("something wrong with j!\n"); break; default: printf ("j = %d (5)\n",j); break; } case 8 : printf ("something wrong with i!\n"); break; default: printf ("i = %d (4)\n",i); break; } } > Or I could even add a 'goto default'......... > (Note: my C Ref Man doesn't say that default is a reserved word, > so using default as an ordinary label is perfectly legal) No you couldn't because default is a reserved word, so either is your C Ref Man corrupted, or you maybe had overlooked the section where the keywords is listed (-: However If your C Ref Man does miss this section I have printed it below... C Reference Manual Dennis M. Ritchie Bell Laboratories Murray Hill, New Jersey 07974 May 1, 1977 2.3 Keywords The following identifiers are reserved for use as keywords, and may not be used otherwise: int extern else char register for float typedef do double static while struct goto switch union return case long sizeof default short break entry unsigned continue auto if The keyword entry is not currently implemented by any compiler but is reserved for future use. Some imple- mentations also reserve the word fortran. Kim Chr. Madsen. Dept. of Computer Science University of Copenhagen Denmark. ------------------------------ UUCP: ...mcvax!diku!kimcm
keesan@bbncca.ARPA (Morris Keesan) (06/20/84)
-------------------------------------------- > What does > > switch(i) { > ... > switch(j) { > ... > default: ... > } > } > > do if there is no case corresponding to i? > . > . > . > Or I could even add a 'goto default'......... > (Note: my C Ref Man doesn't say that default is a reserved word, > so using default as an ordinary label is perfectly legal) > > Jack Jansen, {philabs!decvax}!mcvax!vu44!jack Well, first off, you have a defective "C Ref Man", because the C Reference Manual in K&R clearly lists "default" as a reserved word (section 2.3, Keywords, page 180 of K&R). Secondly, what happens is clearly defined (section 9.7, Switch Statement): Any statement within the statement may be labeled with one or more case prefixes . . . There may also be at most one statement prefix of the form default: If no case matches and if there is no default then none of the statements in the switch is executed. The "default" in the example above is not a prefix of a "statement within the statement", but a prefix of a statement within a statement within the statement. The default will never be considered unless the switch(j) statement is being executed. The answer to the question is that the above fragment evaluates i, compares its value to any case constants (assumed to be in the ...), and then does nothing else. -- Morris M. Keesan {decvax,linus,wjh12,ima}!bbncca!keesan keesan @ BBN-UNIX.ARPA
duk@vu44.UUCP (Duk Bekema) (06/22/84)
In what place in the manual is stated that default (and case)
belongs to the nearest enclosing switch?
Of course, it is logical, it is exactly what I want, and I've
never thought otherwise; but I just can't find it.
This piece of program will print `Got here':
switch (3) {
default:
if (0) {
case 3: printf("Got here\n");
break;
}
break;
}
but this piece won't:
switch (3) {
default:
switch (0) {
case 3: printf("Got here\n");
break;
}
break;
}
Duk Bekema
..!mcvax!vu44!dukjack@vu44.UUCP (Jack Jansen) (06/25/84)
This has probably been discussed before, as everything has,
but here goes :
What does
switch(i) {
...
switch(j) {
...
default: ...
}
}
do if there is no case corresponding to i?
I can imagine even worse constructions like
switch(i) {
switch(j) {
default:....
}
switch(k) {
default:....
}
}
Or I could even add a 'goto default'.........
(Note: my C Ref Man doesn't say that default is a reserved word,
so using default as an ordinary label is perfectly legal)
Jack Jansen, {philabs!decvax}!mcvax!vu44!jack