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 # Example 16: User-Defined Operand (UDOC)

 Last update: 09.03.2026 

Ex 16: A user-defined operand (UDOC) is created which provides the total center thickness between 2 surfaces. Since a UDOC is an executable that needs to be called from OpticStudio, a UDOC can only be created by languages which can compile code (C#/C++). The source code is provided, but it needs to be compiled with the USER OPERAND solution rather than the standalone application solution. The EXE also needs to be named UDOC##.exe and placed in the ZOS-API\\Operands folder.

```
Input:		None

Output:		UDOC01.exe

```

[C#](example_16_cs.md)

[C++](example_16_cpp.md)