Clear way to write if statement

Question

Consider this code:

if (results.Contains(14))
{
    //anything
}
else if (results.Contains(15))
{
    //anything
}
else if (results.Contains(16))
{
    //anything
}

I want write this code with switch case :

switch (results)
{
    case results.Contains(14):
}

But we can't write this in C#.

What is the clear way for write the above code, knowing that results is a long[]?

What is the type of "results"? Is it derived from ICollection, like List? — kol, Aug 13 '13 at 13:02
@pylover yes i dont want just use switch.my question is clear way to write — , Aug 13 '13 at 13:04
@ShahroozJefriㇱ: Are you always display the same `exception`?? — huMpty duMpty, Aug 13 '13 at 13:06

ganders · Answer 1 · 2013-08-13T13:12:27.943

8

What's wrong with this:

if (results.Contains(14) || results.Contains(15) || results.Contains(16))
{
  new Exception("anything");
}

edited Aug 13 '13 at 13:12

answered Aug 13 '13 at 13:05

ganders

7,285
17
66
114

Ah, I see the question was updated to throw an exception with the value that you're checking in the contains, which makes this answer not relevant anymore... – ganders Aug 13 '13 at 13:06
Please update your answer – Aug 13 '13 at 13:11

score 4 · Answer 2 · answered Aug 13 '13 at 13:06

since it is probably in a string that has that number one solution would be to use a regular expression.

var m = System.Text.RegularExpressions.Regex.Matches(results, @"\d{1,2}")[0];
throw new Exception(m);

(NOTE: I did this in notepad so it might require a small tweak)

You will have to probably play with the match syntax as this is only good for 1-2 numbers. in a string.

Zdeslav Vojkovic · Answer 3 · 2013-08-13T14:56:32.303

What are you really trying to do?

The following should work, but I am not sure if that's what you had in mind:

int[] values = {14, 15, 16};
foreach (var n in values) {
  if(result.Contains(n)) 
     throw new Exception(n.ToString()) 
}

-- EDIT: the question has changed considerably so here's an update --

I would probably use plain if-else but if you have many options or complex logic (e.g. not just results.Contains()), sometimes it is better to choose tables:

int[] results = {13, 14, 15};
action_map = new Dictionary<int, Action>();
action_map[14] = () => Console.Out.WriteLine("14");
action_map[15] = () => Console.Out.WriteLine("15");
action_map[16] = () => { throw new InvalidOperationException(); };
action_map[0] = () => {}; // NOP, default case - executed if no match found

var action_key = dict.Keys.FirstOrDefault(k => results.Contains(k));
action_map[action_key]();

In real code, I would probably wrap it into a class:

var table = new FnTable();
table.Add(14, () => Console.Out.WriteLine("14"));
table.Add(15, () => Console.Out.WriteLine("15"));
table.Add(16, () => { throw new InvalidOperationException(); });

int[] results = {13, 14, 15};
table.ExecuteFirstFrom(results);

I think you can remove the part 'if(result.Contains(n))', and use 'result' instead of 'values'. — Kai Hartmann, Aug 13 '13 at 13:42
@KaiHartmann that would affect the order of checks. they have to be done in order defined in `values` not `results`. if `results` is `{16, 15, 14}` then it wouldn't be the same — Zdeslav Vojkovic, Aug 13 '13 at 15:28

score 3 · Answer 4 · edited May 23 '17 at 12:11

3

I like approach with action dictionaries

        var swticher = new Dictionary<long, Func<Exception>>()
        {
            {15,()=>new Exception("15")},
            {14,()=>new Exception("14")}
        };

        throw swticher[14].Invoke();

Of course more complex examples will show power of this approach :)

Why to use dictionaries instead of switches: https://stackoverflow.com/a/11617459/1714342

Abstract:

The short answer is that the switch statement executes linearly, while the dictionary executes logarithmically.

edited May 23 '17 at 12:11

Community

1
1

answered Aug 13 '13 at 13:05

Kamil Budziewski

22,699
14
85
105

Your quote is incorrect. `switch`, in C#, can actually be implemented as a dictionary. That's why all case statements must be compile time constants, rather than any executable expression. Read the complete analysis of your own link for the details. – Servy Aug 13 '13 at 14:16

score 3 · Answer 5 · answered Aug 13 '13 at 13:10

Usually a clear way to replace if/switch statements is to use polymorphism. However, in the example you've provided the if statements are so trivial, that they can be replaced by a simple algorithm which calculates the contents of the exception, as stated in Robert Snyder's answer.

score 2 · Answer 6 · answered Aug 13 '13 at 13:12

2

switch (C# Reference):

Each case label specifies a constant value.

In your expected sample code, results.Contains(14) is not a constant value, so the syntax will not be valid.

answered Aug 13 '13 at 13:12

Alex Filipovici

31,789
6
54
78

huysentruitw · Accepted Answer · 2013-08-13T13:46:04.950

2

You can use a switch statement inside a foreach:

long[] results = new long[] { 15, 14, 16 };
foreach (long v in results)
{
    switch (v)
    {
        case 14:
            // anything
            break;
        case 15:
            // anything
            break;
        case 16:
            // anything
            break;
    }
}

And to better match with your question, you should order the array first and get out the foreach after a match:

long[] results = new long[] { 15, 14, 16 };
Array.Sort(results);
foreach (long v in results)
{
    switch (v)
    {
        case 14:
            // anything
            break;
        case 15:
            // anything
            break;
        case 16:
            // anything
            break;
        default:
            continue; // continue the foreach loop
    }
    break; // break the foreach loop because we had a valid match
}

edited Aug 13 '13 at 13:46

answered Aug 13 '13 at 13:14

huysentruitw

27,376
9
90
133

2

Dictionaries are better solution: http://stackoverflow.com/a/11617459/1714342 – Kamil Budziewski Aug 13 '13 at 13:15
@wudzik: I think my answer better matches the (updated) question. The latter example in my answer is a drop in replacement for what the OP wants. – huysentruitw Aug 13 '13 at 13:26
I like your answer, but it does not have to be a lambda expression. It could simply be: foreach (long v in array) { switch (v) { case 14: break; case 15: break; case 16: break; } } – Kai Hartmann Aug 13 '13 at 13:39
@KaiHartmann you're right, it was overkill, removed it. Thanks. – huysentruitw Aug 13 '13 at 13:46

Paolo Falabella · Answer 8 · 2013-08-13T13:36:47.457

I would not actually recommend to do it this way, but if you're really into switch statements...

long? CheckSpecialNumbers(long[] res)
{
    var specialNumbers = new List<long>() {14, 15, 16};
    var inters= specialNumbers.Intersect(res);
    return inters.Count() > 0 ? (long?)inters.First() : null;
}

then you could do:

long? res = CheckSpecialNumbers(results);

switch (res)
{
    case 14:
        Console.WriteLine(14);
        break;
    case 15:
        Console.WriteLine(15);
        break;
    case 16:
        Console.WriteLine(16);
        break;
}

kol · Answer 9 · 2013-08-13T13:31:33.540

1

I want write this code with switch case

A switch-case statement is used to branch the execution path according to the value of a given variable. The OP wants to branch according to the value of a Boolean expression, specifically, the return value of Contains. This can only be done using an if-else statement. Writing switch (results) doesn't make sense, since results is an array of integers.

edited Aug 13 '13 at 13:31

answered Aug 13 '13 at 13:18

kol

27,881
12
83
120

Clear way to write if statement

9 Answers9