What is the difference between String and string in C#
In C#, string (lowercase) is a keyword and an alias for the System.String class. String (uppercase) is the actual .NET class name. Both are functionally identical and compile to the same IL code.
Most C# developers prefer using string (lowercase) as it follows the language's convention for built-in types like int, bool, and double.
The C# coding conventions recommend using the keyword alias when available.
C# Example Code
using System;
// Both declarations are identical
string lowerCase = "Hello World";
String upperCase = "Hello World";
// They are the same type
Console.WriteLine(lowerCase.GetType()); // System.String
Console.WriteLine(upperCase.GetType()); // System.String
// ReferenceEquals proves they're the same type
Console.WriteLine(lowerCase.GetType() == upperCase.GetType()); // True
// Both have access to the same methods
Console.WriteLine(lowerCase.ToUpper()); // HELLO WORLD
Console.WriteLine(upperCase.ToLower()); // hello world
// Convention: use lowercase 'string'
string preferredStyle = "Use this style";
Console.WriteLine(preferredStyle);