Ask about switch

Please help me. I have code as following

Code:

---

#include <stdio.h>

int main()
{
        int num = 1;
                switch (num)
                {
                case 1, 3, 5://causes error - (1)
                        printf("Even");
                        break;
                case 6..7://causes error - (2)
                        printf("Unknown");
                        break;
                default:
                        printf("Ok");
                }
        return 0;
}

---

Why (1) and (2) cause errors. In switch of C, doesn't support multiple const and interval constant ?

cases must be listed separately:

Code:

---

switch (num)
                {
                case 1:
                case 3:
                case 5://causes error - (1)
                        printf("Even");
                        break;
                case 6:
                case 7://causes error - (2)
                        printf("Unknown");
                        break;
                default:
                        printf("Ok");
                }

---

and no it does not support intervals like that (although that's not even really a valid interval)

GCC has case intervals IIRC, but it is very much a compiler extension.

If you use it, you´ll be tying yourself to a single compiler.

So bad. If I want to put in integer number, and check if it equals 1, 3, 5, 7, 8, 10, 12 -> printf("has 31 days")... I mean use many case statement. So bad for C and C++.

Quote:

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Originally Posted by rags_to_riches

cases must be listed separately:

Code:

---

switch (num)
                {
                case 1:
                case 3:
                case 5://causes error - (1)
                        printf("Even");
                        break;
                case 6:
                case 7://causes error - (2)
                        printf("Unknown");
                        break;
                default:
                        printf("Ok");
                }

---

and no it does not support intervals like that (although that's not even really a valid interval)

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Write it with if -- the other kind of branching logic -- and see if it makes more sense to you, I guess.

It looks to me like you want to print how many days exist in each month. Just setup and array with 12 slots...and put array[0] = 30...then its easy. printf(%u\n",array[number]);

Of course this is assuming that's what you are trying to do...

Quote:

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Originally Posted by micheal9000

So bad. If I want to put in integer number, and check if it equals 1, 3, 5, 7, 8, 10, 12 -> printf("has 31 days")... I mean use many case statement. So bad for C and C++.

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I don't see how you would think this a bad thing... It's more typing for the programmer but the final code from my compiler is pretty compact. switch() has it's place, especially in Windows where it's used very heavily for handling window messages. Call it a convenience for picking multiple branches...

If you're looking for lists or ranges (a la Pascal) then you need switch()'s ugly stepsister if() ... else if()... in which case you can put any valid conditional statement you like into your branching code.