Referencing a variable, method, or class name that compiler cannot find in scope.
C# compiler error CS0103 indicates that an identifier used in the code cannot be resolved within the current scope or imported namespaces.
Typos in variable/method names, missing `using` directives for required namespaces, or declaring a variable inside an `if` block and accessing it outside.
1using System;2 3public class Program {4 public static void Main() {5 // Missing: using System.Text;6 StringBuilder sb = new StringBuilder(); // Error CS0103: The name 'StringBuilder' does not exist in the current context7 }8}1using System;2using System.Text; // Add missing namespace directive3 4public class Program {5 public static void Main() {6 StringBuilder sb = new StringBuilder();7 sb.Append("Fixed!");8 Console.WriteLine(sb.ToString());9 }10}Simulate standard system builds to trigger compiler trace records and track memory crashes locally.
`StringBuilder` belongs to the `System.Text` namespace. Without `using System.Text;`, the compiler cannot resolve `StringBuilder`.