peternilsson42 wrote:
>
>
>
> --- In [email protected] <mailto:c-prog%40yahoogroups.com>, ayyaz
> <ayya...@...> wrote:
> > Steve Searle wrote:
> > > ayyaz scrawled:
> > > > switch (choice = getchar()) {
> > > > case 'r':
> > > >
> > > > case 'R':
> > > > printf("RED");
> > > > break;
> > > >
> > > > case 'w':
> > > >
> > > > case 'W':
> > > > printf("WHITE");
> > > > break;
> > > > }
> > > >
> > > > Should it not only output 'RED' or 'WHITE' when you
> > > > enter 'R' or 'W'?
> > >
> > > You don't have a break following the case 'r': and
> > > case 'w': statements. So control passes to the next
> > > statement - the corrosponding upper case ones.
> >
> > 1) Why does control pass it to the next statement when
> > the next statement is 'R' which is not equivalent to 'r'?
>
> Because 'case' labels are just labels. Switches are like
> big 'goto's. If something matches the case, then 'goto'
> that statement.
>
> C allows you to label any statement. It doesn't limit how
> many labels you have for a given statement, though case
> labels must appear inside of a switch statement.
>
> Consider the following...
>
> int foo(int n, const int a[], int x)
> {
> int i, j, s;
>
> for (i = 0; i < n; i++)
> {
> for (s = j = 0; j <= i; j++)
> {
> if ( a[j] <= 0
> || a[j] > (INT_MAX - s) / a[j] )
> {
> i = -1;
> goto err;
> }
>
> s += a[j] * a[j];
> if (s >= x)
> goto fin;
> }
> }
>
> err:
> fin:
> return i;
> }
>
> Here, I've labelled the final return statement twice. There
> are two cases where I want to jump to it: on error, and on
> success.
>
> Case labels are no different. You can (almost) have as many
> as you want. They don't mark separate blocks of statements,
> they just mark individual statements that code can jump to.
>
> Note that labels _must_ mark statements. You can't have a
> label on its own...
>
> void foo(void)
> {
> ... processing that does goto fin; ...
> fin:
> }
>
> You need...
>
> void foo(void)
> {
> ... processing that does goto fin; ...
> fin:
> ; /* null statment lebelled fin */
> }
>
> Once you understand that case labels are just labels, and
> you can have many marking the same statement, then the
> jump to and flow through effects of switch statements
> become clearer...
>
> case 'r': case 'R': /* come here if r or R */
> printf("RED");
> break;
> case 'w': case 'W': /* come here if w or W */
> printf("WHITE");
> break;
>
> --
> Peter
>
>
Hello,
Thanks all for the help. I now understand that case labels are just
labels so any number of labels can be assigned to some statement.
I have written the following code.
#include <stdio.h>
int main(void)
{
char color;
while (1) {
printf("\nPlease enter color: ");
scanf("%c",&color);
switch (color) {
case 'r':
case 'R':
printf("\nRed");
break;
case 'g':
case 'G':
printf("\nGreen");
break;
case 'b':
case 'B':
printf("\nBlue");
break;
default:
printf("\nBlack");
break;
}
}
}
Basically it just prints Red, Green, Blue, or Black depending on what
the user enters. If the user enters anything besides RGB, then it prints
black. It works if I don't have a while loop but with the while loop the
default label always gets evaluated. What is the reason for this?
Thanks,
--ayyaz
