Reputation: 1

Doubts in using switch statement in C

I have a doubt: why am I getting outputs when i=3 and when i=7?

main()
{
  int i;
  scanf("%d",&i);
  switch(i)
  {
        case 3: printf("message3");
        default:
               if(i==4)
               printf("message4");
        case 2:printf("message2");
               break;
        case 1:printf("Message1");
  }
}

Upvotes: 0

Answers (5)

pmg

Reputation: 108968

The order of the default case does not determine when that case is executed. The default case is executed when the switch variable does not match any of the values in a case expression.

For the code above a value of

1 will print "Message 1" when executing the code following the case 1
2 will print "message 2" when executing the code following the case 2
3 will print "message 3message2" when executing the code following the case 3 and fallthrough to default and fallthrough to case 2
4 will print "message 4message2" when executing the code following the default and fallthrough to case 2
any other value will print "message 2" when executing the default case and fallthrough to case 2

I some times code my switches with the default first

switch (ch) {
  default: break; /* do nothing */
  case '.': ch = ','; break; /* swap commas */
  case ',': ch = '.'; break; /* and periods */
}

Upvotes: 0

Bhaskar

Reputation: 2723

@Shubham. Please forgive me if I am repeating what you already know. And in some ways, I am expanding what @Henk already pointed out.

In switch statement, the role of case and default labels are only to determine where the execution should start. Once the first label is determined then rest of the labels have no meaning. The execution is "fall through". Therefore, we have to use break to stop and exit the switch.

In your code, if i == 3 then case 3 is the first line of execution. Then case 3, default and case 2 are executed followed by break.

If i is any value other than 3 then default is executed followed by case 2 and then exit the switch. I don't think one will ever get to execute case 1 due to the location of default.

Upvotes: 2