Compare strings in C# in switch-case block with different casing

Question

I have a set of switch-case statements, such as "Hello, how are you", "Hi, how can I help you?". If the input from the user is verbatim i.e: "Hello, how are you", the match works.

But if the user entered "Hello, How are You", the match fails.

I would like if the user's input is the same but different casing then it should match. i.e.

"Hello, how are you" == "Hello, How are You" == "HELLO, how are YOU"

How can this be accomplished?

`switch` would likely be the wrong tool for the job. However you could always just ToLower() the strings. Though i feel the next question would be, how do i deal with extra spaces or punctuation — TheGeneral, Jun 22 '20 at 05:07
I cannot lowercase the switch statements because they are shown elsewhere on the UI and hence casing should be maintained. — user1144596, Jun 22 '20 at 05:10
The ToLower() will be applied only for comparison. It won't modify the string to be displayed. — Jaime, Jun 22 '20 at 05:15
If you `switch (yourValue.ToLower())`, nothing outside the switch is impacted by the ToLower - that doesn't necessarily make it a good approach though; I'm just saying that "because they are shown elsewhere on the UI" is irrelevant — Marc Gravell, Jun 22 '20 at 05:17
Take a look at my answer to this https://stackoverflow.com/questions/2334134/how-to-make-the-c-sharp-switch-statement-use-ignorecase/51794712#51794712 — Flydog57, Jun 22 '20 at 05:20

score 6 · Answer 1 · answered Jun 22 '20 at 05:21

If you are using C# 7.0 or newer then you can use Pattern Matching with switch..case like below.

string a = "Hello, How are You";

switch (a)
{
    case string str when str.Equals("hello, how are you", StringComparison.InvariantCultureIgnoreCase):
        // Your code
        break;
    default:
        // default code
        break;

}

score 2 · Answer 2 · answered Jun 22 '20 at 05:09

2

Just use ToLower on everything to do a non-case sensitive switch:

switch (myString.ToLower())
{
    case "hello, how are you":
        // do something
        break;
}

answered Jun 22 '20 at 05:09

trinalbadger587

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3

This is not an allocation-friendly way of comparing strings – Marc Gravell Jun 22 '20 at 05:10

score 2 · Answer 3 · answered Jun 22 '20 at 05:15

The switch handler in C# for strings is limited to exact character matching. Ultimately there are three approaches here:

use if, not a switch, and make use of manual string equality tests - perhaps specifying a StringComparison for case insensitivity
create a dictionary (perhaps static) with a case insensitive key comparer; put your expected strings in the dictionary - perhaps mapping to a private enum output, then switch on that output
use ToLower[Invariant] in the switch operand, and just eat the allocation

If it isn't high throughput, the last is probably fine

@Karan well, yes, but a `switch` expression that uses `when` for every meaningful test is really no different to a series of `if`, `else` tests - just shoe-horned into the `switch` syntax for the sake of it... — Marc Gravell, Jun 22 '20 at 05:41

score 0 · Answer 4 · answered Jun 22 '20 at 05:17

Instead of converting both strings to upper case or lower case and then comparing, you should use an equality comparison which can be made case-insensitive. For example:

String string1 = "Hello, how are you";
if (string1.Equals("Hello HOW are you", StringComparison.OrdinalIgnoreCase))
{
     ...
}
You should consider carefully exactly which rules are appropriate - ordinal, the current culture, the invariant culture, or possibly another culture entirely (e.g. using StringComparer.Create(culture, true)).

Compare strings in C# in switch-case block with different casing

4 Answers4