Switch case, check ranges in C# 3.5

Question

In C#, the switch statement doesn't allow cases to span ranges of values. I don't like the idea of using if-else loops for this purpose, so are there any other ways to check numeric ranges in C#?

You can't really do it in C# (unless it's a small range of numbers you can list in blocks), but, for once, you **can** in VB.Net - http://stackoverflow.com/questions/1009902/select-case-to-check-range-of-a-decimal-number funnily enough — dash, Jul 05 '12 at 06:58
Well you can have a method returning bool which takes in the range and then if loops, its simple, readable and does the work well — V4Vendetta, Jul 05 '12 at 06:58
http://stackoverflow.com/questions/68578/multiple-cases-in-switch You cannot do this in C#. Check the answer above. — Dzung Nguyen, Jul 05 '12 at 07:22
**Important note** : Ranges are supported in switch case starting C# v7 - [Switch case: can I use a range instead of a one number](https://stackoverflow.com/q/20147879/465053). So, if you feel like better upgrade from C# v3.5 to v7 instead. — RBT, May 18 '18 at 11:45

score 16 · Accepted Answer · edited Mar 15 '14 at 16:24

16

You can use a HashTable respectively Dictionary to create a mapping of Condition => Action.

Example:

class Programm
{
    static void Main()
    {
        var myNum = 12;

        var cases = new Dictionary<Func<int, bool>, Action>
        { 
            { x => x < 3 ,    () => Console.WriteLine("Smaller than 3")   } ,
            { x => x < 30 ,   () => Console.WriteLine("Smaller than 30")  } ,
            { x => x < 300 ,  () => Console.WriteLine("Smaller than 300") } 
        };

        cases.First(kvp => kvp.Key(myNum)).Value();
    }
}

This technique is a general alternative to switch, especially if the actions consists only of one line (like a method call).

And if you're a fan of type aliases:

using Int32Condition = System.Collections.Generic.Dictionary<System.Func<System.Int32, System.Boolean>, System.Action>;
...
    var cases = new Int32Condition()
    { 
        { x => x < 3 ,    () => Console.WriteLine("Smaller than 3")   } ,
        { x => x < 30 ,   () => Console.WriteLine("Smaller than 30")  } ,
        { x => x < 300 ,  () => Console.WriteLine("Smaller than 300") } 
    };

edited Mar 15 '14 at 16:24

Saverio Terracciano

3,885
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answered Jul 05 '12 at 07:08

sloth

99,095
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2

But you should not take a dictionary (take a list of KeyValuePair, Tuple or sth self defined) otherwise you can't predict in which order the Funcs are called for testing. – Oliver Jul 05 '12 at 08:19
1

Interesting but if I saw this pattern as a replacement of if/else in real project I'm submitting it to http://thedailywtf.com :) – Stilgar Jul 05 '12 at 08:23
This solution is outright ridiculous. Good for a quiz, but very bad for production code. It is slow, as it wastes memory, and causes too much calls which cannot be inlined. – Nick Jul 05 '12 at 08:28
This code doesn't even *work*. Since a dictionary is inierently unordered you can't be sure that `x < 3` will be checked before `x < 30`. That it does in one or two tests cases doesn't mean it will hold true. A `Dictionary` is simply the wrong data structure here, unless you ensure that the methods can be called in any order (which you haven't done). As mentinoed by Oliver, a list of tuples would be one way to ensure ordering, and is semantically correct. Note that this isn't really any different than a series of `if/else if` statements either. – Servy Jun 21 '13 at 14:50

score 5 · Answer 2 · answered Jul 05 '12 at 06:56

5

Nope. Of course, if the ranges are small you could use the

case 4:
case 5:
case 6:
   // blah
   break;

approach, but other than that: no. Use if/else.

answered Jul 05 '12 at 06:56

Marc Gravell

1,026,079
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score 4 · Answer 3 · answered Jul 05 '12 at 06:58

if the interval of the ranges is constant, you can try

        int num = 11;
        int range = (num - 1) / 10; //here interval is 10
        switch (range)
        {
            case 0:
                Console.Write("1-10");
                break; // 1-10
            case 1:
                Console.Write("11-20");
                break; // 11-20
            // etc...
        }

Output would be: "11-20"
if interval is variable then use if/else

Stilgar · Answer 4 · 2013-02-02T16:07:46.103

1

No. At least nothing which is more beautiful.

Also there is no C# 3.5 only .NET 3.5 and C# 3.0

edited Feb 02 '13 at 16:07

answered Jul 05 '12 at 06:57

Stilgar

22,354
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score 1 · Answer 5 · answered Jul 05 '12 at 07:10

Try something like this

 private void ExecuteInRange(Dictionary<Range,Action<int>> ranges)
    {
        foreach (var range in ranges)
        {
            if (range.Key.Value < range.Key.Max && range.Key.Value > range.Key.Max)
                range.Value(range.Key.Value);
        }
    }


public class Range
{
    public int Min { get; set; }
    public int Max { get; set; }
    public int Value { get; set; }
}

score 1 · Answer 6 · answered Jun 24 '13 at 13:15

        int b;
        b = Int32.Parse(textBox1.Text);

        int ans = (100-b)/3; //the 3 represents the interval
        //100 represents the last number


        switch(ans)
        {

           case 0:
                MessageBox.Show("98 to 100");
           break;

           case 1:
                MessageBox.Show("95 to 97");
           break;

           case 2:
                MessageBox.Show("92 to 94");
           break;

           case 3:
                MessageBox.Show("89 to 91");
           break;

           case 4:
                MessageBox.Show("86 to 88");
           break;

           default:
                MessageBox.Show("out of range");
           break;

score -1 · Answer 7 · answered Jun 21 '13 at 14:46

-1

A sort of nested-shorthand if-else thing works, and is clean.

myModel.Value = modelResult >= 20 ? 5 : modelResult >= 14 ? 4 : modelResult >= 5 ? 3 : modelResult >= 2 ? 2 : modelResult == 1 ? 1 : 0;

answered Jun 21 '13 at 14:46

blomster

768
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Switch case, check ranges in C# 3.5

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