How to compare two strings and their upper and lower case signs

Question

Let's say I have 2 strings. First string is x = "abc" and the second one is y = "ABC". In C# when I write the following code:

if (x == y)

or

if (x.Equals(y))

the return value is true. How can I check their upper and lower case?

Answer 1

The return value is not true but false since .NET is case sensitive by default.

From String.Equals:

This method performs an ordinal (case-sensitive and culture-insensitive) comparison.

For == the same is true since String.Equality operator calls Equals:

This operator is implemented using the Equals method, which means the comparands are tested for a combination of reference and value equality. This operator performs an ordinal comparison.

This will compare case insensitively:

bool equals = x.Equals(y , StringComparison.OrdinalIgnoreCase);

If you just want to know if a character is upper or lower case you can use these methods:

bool isUpperChar = Char.IsUpper("ABC"[0]); // yes
bool isLowerChar = Char.IsLower("ABC"[0]); // no

Answer 2

First, you should decide whether you compare strings in culture dependent or independent way (e.g. in Russian Culture letters "E" and "Ё" often treats as being the same; Finnish tends to treat "V" and "W" as being the same etc.). Next you should choose whether use or not use case ("a" v. "A"). So there're 6 possible comparisons:

Ordinal (culture independent) comparisons:

// Ignore case comparison
Boolean equals = String.Equals(x, y, StringComparison.OrdinalIgnoreCase);
// Case comparison
Boolean equals = String.Equals(x, y, StringComparison.Ordinal);

Current culture comparisons:

// Current culture, ignore case comparison
Boolean equals = String.Equals(x, y, StringComparison.CurrentCulture);
// Current culture, case comparison
Boolean equals = String.Equals(x, y, StringComparison.CurrentCultureIgnoreCase);

Explicit culture comparisons:

CultureInfo culture = new CultureInfo("Ru-ru"); // <- Or whatever you want

// Explicit culture, ignore case comparison
Boolean equals = culture.CompareInfo.Compare(x, y, CompareOptions.IgnoreCase);
// Explicit culture, case comparison
Boolean equals = culture.CompareInfo.Compare(x, y, CompareOptions.None);