What’s the difference between double quotes and single quote in C#?

Single quotes encode a single character (data type char), while double quotes encode a string of multiple characters. The difference is similar to the difference between a single integer and an array of integers.

char c="c";
string s = "s"; // String containing a single character.
System.Diagnostics.Debug.Assert(s.Length == 1);
char d = s[0];

int i = 42;
int[] a = new int[] { 42 }; // Array containing a single int.
System.Diagnostics.Debug.Assert(a.Length == 1);
int j = a[0];