converting an if statement to a switch statement

Question

How can I convert the following if=statement to a switch-statement WITHOUT needing to create a case for every number between that interval (41-49)? Is it possible?

if (num < 50 && num > 40)
{
    printf("correct!");
}

In what language? C? C++? Something else? – Oded Jul 07 '11 at 20:23 — Oded, Jul 07 '11 at 20:23
And _why_ would you want to convert such an expression? – Oded Jul 07 '11 at 20:24 — Oded, Jul 07 '11 at 20:24

score 1 · Answer 1 · answered Jul 07 '11 at 20:29

You have to enumerate every case for a switch. The compiler converts this to a jump table, so you can't use ranges. You can, however, have multiple cases use the same block of code, which may be closer to what you want.

switch(num) {
    case 41:
    case 42:
    case 43:
    case 44:
    case 45:
    case 46:
    case 47:
    case 48:
    case 49:
        printf("correct!");
        break;
    default:
        break;
}

score 1 · Answer 2 · answered Jul 07 '11 at 20:34

1

What about this?

switch ((num-41)/9) {
case 0:
    printf("correct!");
    break;
}

answered Jul 07 '11 at 20:34

phlogratos

13,234
1
32
37

score 0 · Answer 3 · answered Jul 07 '11 at 20:24

0

bool criteria1 = (num < 50 && num > 40);
switch criteria1: ...

It may result in multilevel decision networks.. scary?

answered Jul 07 '11 at 20:24

kagali-san

2,964
7
48
87

are booleans the only way to do this? is there another method? can i attach conditions to the case instead? just curious. – wadafarfar Jul 07 '11 at 20:40
@wadafarfar, if your desired language supports returning true|false values when evaluating (...) and they are seen by switch statement - then, yes. `switch (condition) true: code1; false: code2; end;` will work. Write a test for that? – kagali-san Jul 07 '11 at 21:06

score 0 · Answer 4 · answered Jul 07 '11 at 20:26

In C or C++ (since you are using printf, I'll assume that's what it is), cases need to be enumerated for each choice.

The only difference between switch/case and if is the possibility that the compiler can turn it into a computed goto instead of checking ranges. If switch/case supported ranges, that would defeat the purpose of opening the possibility of this optimizaton.

converting an if statement to a switch statement

4 Answers4