What is the difference between Compare() and CompareTo() for strings in C#?

I know it returns integer but I needed to know on what basis.

Example:

string s1 = "world";
string s2 = "World";

Console.WriteLine(string.Compare(s1,s2));   

Console.WriteLine(s1.CompareTo(s2));

it returns -1 for both. But if we capitalize w in s1 and lowercase w in s2 it returns 1.

So need some explanation for it.

We can see the difference when one (or both strings) is null:

string s1 = null;
string s2 = "World";

// -1, since null < "World"
Console.WriteLine(string.Compare(s1,s2));   

// NullReferenceException thrown, attempt to call null.CompareTo("World")
Console.WriteLine(s1.CompareTo(s2));

If we are talking about behaviour then they are the same and both under the hood call same static int string.Compare with defaulted StringComparison.CurrentCulture.

The main difference lies in static method vs instance method. So s1.CompareTo(s2) throw NullReferenceException if s1 is null.

In C#, both the Compare() and CompareTo() methods are used for string comparisons, but they have different implementations and return types.

1. Compare() Method:

• The Compare() method is a static method of the string class in C#. It
  compares two strings and returns an integer that indicates their
  relative order in terms of sorting.
• The return value of Compare() is an integer less than 0 if the first
  string is less than the second, 0 if they are equal, or an integer
  greater than 0 if the first string is greater than the second.
• It allows you to perform case-sensitive or case-insensitive
  comparisons based on the specified StringComparison enumeration
  value.
• The Compare() method can be useful for sorting and ordering
  operations.

Example usage of Compare():

string string1 = "apple";
string string2 = "banana";
int result = string.Compare(string1, string2);

2. CompareTo() Method:

• The CompareTo() method is an instance method of the string class in
  C#.
• It compares the current string instance with another string and
  returns an integer that indicates their relative order in terms of
  sorting.
• The return value of CompareTo() is similar to Compare(): less than 0
  if the current string is less than the other, 0 if they are equal, or
  greater than 0 if the current string is greater.
• It performs a case-sensitive comparison by default but can be used
  with the StringComparison enumeration to specify case-insensitive
  comparisons.
• The CompareTo() method is typically used for natural sorting or when
  comparing strings in an object-oriented manner.

Example usage of CompareTo():

string string1 = "apple";
string string2 = "banana";
int result = string1.CompareTo(string2); 

Both Compare() and CompareTo() can be used to compare strings, but Compare() is a static method that accepts two string parameters, while CompareTo() is an instance method called on a single string instance.