C#: Confusion about ToUpper() and ToLower()

c# string-comparison
Serenity picture Serenity · Sep 12, 2010 · Viewed 15.7k times · Source

if I do something like this...

String myVar = "in";
if(myVar.ToUpper() == "in")
{
    //do something
}

This is not going to go inside "if" block ..right?

or

Is it going to check BOTH for "in" AND "IN" and do whatever is there inside that if? If so, why is that ? Isn't it supposed to skip what's inside of "if" block?

Same confusion is about ToLower() too

Edit: So to check for both cases, I need to write:

if((myVar.ToUpper().Equals("in"))&&(myVar.Equals("in")))

Like this..right?

Answer

Jon Skeet picture Jon Skeet · Sep 12, 2010

Rather than converting to upper case and then comparing, you should use an equality comparison which can be made case-insensitive. For example:

if (myVar.Equals("in", 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)).

For more details around this, read the MSDN Best Practices for Using Strings in the .NET Framework article.

Related questions

How can I do a case insensitive string comparison?

How can I make the line below case insensitive? drUser["Enrolled"] = (enrolledUsers.FindIndex(x => x.Username == (string)drUser["Username"]) != -1); I was given some advice earlier today that suggested I use: x.Username.Equals((string)drUser["Username"], StringComparison.OrdinalIgnoreCase))); …

Read More
Difference between InvariantCulture and Ordinal string comparison

When comparing two strings in c# for equality, what is the difference between InvariantCulture and Ordinal comparison?

Read More
Comparing strings with tolerance

I'm looking for a way to compare a string with an array of strings. Doing an exact search is quite easy of course, but I want my program to tolerate spelling mistakes, missing parts of the string and so on. …

Read More