How to Select a Range of Values in a Switch Statement

How do I select a range of values in a switch statement?

In C++ case labels are constant expressions, not expressions in general. You need a chain of if-then-else statements to do what you are trying to do.

Alternatively, you can enumerate the values in the switch. This runs marginally faster (though it does not matter in cases like yours), but it is considerably less readable:

switch(score) {
    case 0: cout << "f"; break;
    case 1:
    case 2:
    case 3:
    case 4:
    case 5:
    case 6:
    case 7:
    case 8:
    case 9:
    case 10: cout << "e"; break;
    case 11:
    case 12:
    case 13:
    case 14:
    case 15:
    case 16:
    case 17:
    case 18:
    case 19:
    case 20:
    case 21:
    case 22:
    case 23:
    case 24:
    case 25: cout << "c"; break;
    // ...and so on, you get the idea...

}

Using switch statement with a range of value in each case?

Java has nothing of that sort. Why not just do the following?

public static boolean isBetween(int x, int lower, int upper) {
  return lower <= x && x <= upper;
}

if (isBetween(num, 1, 5)) {
  System.out.println("testing case 1 to 5");
} else if (isBetween(num, 6, 10)) {
  System.out.println("testing case 6 to 10");
}

In C++ can there be a range of values in a switch statement?

Switch case in C is really just a computed goto, not a comparison and jump to the next case if condition isn't match so it can't support case comparisons like that.

Besides your example is incorrect. If C < 60 the score will match all 4 cases, so where will it jump? Same to C < 70 when it matches 3 cases and so on.

GCC supports case ranges extension but not like you expected. Anyway you may still use that if needed

switch (score)
{

case 0 ... 59:
    cout << "F";
    break;

case 60 ... 69:
    cout << "D";
    break;

case 70 ... 79:
    cout << "C";
    break;

case 80 ... 89:
    cout << "B";
    break;

case 90 ... 100:
    cout << "A";
    break;

default:
    cout << "Out of range\n";
}

Of all the languages I know, only Visual Basic supports comparisons in cases like

Select Case score
    Case Is >= 0 And Is < 60

    Case Is >= 60 And Is < 70

    Case Is >= 70 And Is < 80

    Case Is >= 80 And Is < 90

    Case Is >= 90 And Is <= 100

    Case Else
End Select

However the better way to get the range is to divide the score by 10

const char* SCORE[] = "FDCBA";
if (score < 60)
    cout << SCORE[0];
else if (score < 100);
    cout << SCORE[score/10 - 5];
else if (score == 100)
    cout << SCORE[4];

Of course you still need to make sure that scores aren't less than 0 or higher than 100

How can I use ranges in a switch case statement using JavaScript?

You have at least four options:

1. List each case

As shown by LightStyle, you can list each case explicitly:

switch(myInterval){

    case 0:
    case 1:
    case 2:
        doStuffWithFirstRange();
        break;

    case 3:
    case 4:
    case 5:
        doStuffWithSecondRange();
        break;

    case 6:
    case 7:
        doStuffWithThirdRange();
        break;

    default:
        doStuffWithAllOthers();
}

2. Use if / else if / else

If the ranges are large, that gets unwieldy, so you'd want to do ranges. Note that with if...else if...else if, you don't get to the later ones if an earlier one matches, so you only have to specify the upper bound each time. I'll include the lower bound in /*...*/ for clarity, but normally you would leave it off to avoid introducing a maintenance issue (if you include both boundaries, it's easy to change one and forget to change the other):

if (myInterval < 0) {
    // I'm guessing this is an error
}
else if (/* myInterval >= 0 && */ myInterval <= 2){
    doStuffWithFirstRange();
}
else if (/* myInterval >= 3 && */ myInterval <= 5) {
    doStuffWithSecondRange();
}
else if (/* myInterval >= 6 && */ myInterval <= 7) {
    doStuffWithThirdRange();
}
else {
    doStuffWithAllOthers();
}

3. Use case with expressions:

JavaScript is unusual in that you can use expressions in the case statement, so we can write the if...else if...else if sequence above as a switch statement:

switch (true){

    case myInterval < 0:
        // I'm guessing this is an error
        break;    
    case /* myInterval >= 0 && */ myInterval <= 2:
        doStuffWithFirstRange();
        break;

    case /* myInterval >= 3 && */ myInterval <= 5:
        doStuffWithSecondRange();
        break;

    case /* myInterval >= 6 && */ myInterval <= 7:
        doStuffWithThirdRange();
        break;

    default:
        doStuffWithAllOthers();
}

I'm not advocating that, but it is an option in JavaScript, and there are times it's useful. The case statements are checked in order against the value you give in the switch. (And again, lower bounds could be omitted in many cases because they would have matched earlier.) Even though the cases are processed in source-code order, the default can appear anywhere (not just at the end) and is only processed if either no cases matched or a case matched and fell through to the default (didn't have a break; it's rare you want to do that, but it happens).

4. Use a dispatch map

If your functions all take the same arguments (and that could be no arguments, or just the same ones), another approach is a dispatch map:

In some setup code:

var dispatcher = {
    0: doStuffWithFirstRange,
    1: doStuffWithFirstRange,
    2: doStuffWithFirstRange,

    3: doStuffWithSecondRange,
    4: doStuffWithSecondRange,
    5: doStuffWithSecondRange,

    6: doStuffWithThirdRange,
    7: doStuffWithThirdRange
};

Then instead of the switch:

(dispatcher[myInterval] || doStuffWithAllOthers)();

That works by looking up the function to call on the dispatcher map, defaulting to doStuffWithAllOthers if there's no entry for that specific myInterval value using the curiously-powerful || operator, and then calling it.

You can break that into two lines to make it a bit clearer:

var f = dispatcher[myInterval] || doStuffWithAllOthers;
f();

I've used an object for maximum flexibility. You could define dispatcher like this with your specific example:

var dispatcher = [
    /* 0-2 */
    doStuffWithFirstRange,
    doStuffWithFirstRange,
    doStuffWithFirstRange,

    /* 3-5 */
    doStuffWithSecondRange,
    doStuffWithSecondRange,
    doStuffWithSecondRange,

    /* 6-7 */
    doStuffWithThirdRange,
    doStuffWithThirdRange
];

...but if the values aren't contiguous numbers, it's much clearer to use an object instead.

Switch on ranges of integers in JavaScript

Here is another way I figured it out:

const x = this.dealer;
switch (true) {
    case (x < 5):
        alert("less than five");
        break;
    case (x < 9):
        alert("between 5 and 8");
        break;
    case (x < 12):
        alert("between 9 and 11");
        break;
    default:
        alert("none");
        break;
}

Switch Statement with range value

switch statements don't work like that. Your second case is checked like this: if (percent == (percent > 10 && percent < 20)) ..., which will not yield the desired result.

You could use an if / elseif / else construct:

if (percent === 0) {
  widthbytes = 0;
} else if (percent > 10 && percent < 20 {
  widthbytes = 16;
} else if (percent >= 20 && percent < 30 {
  widthbytes = 30;
} else {
  widthbytes = 0;
}

Or you could use a function that turns the ranges into constants:

function getRange(percent) {
  return Math.floor(percent/10);
}

switch(getRange(percent)) {
  case 10:
    widthbytes = 16;
    break;
  case 20:
    widthbytes = 30;
    break;
  default: 
    widthbytes = 0;  
}

Note that to get a cleaner implementation i assimilated your original case 0: into the default, since they both do the same thing. If that is not desirable, you need to change the getRange function to no longer return the same range for 0 as for any number between 0 and 10.

---

Related Topics