There are several features of OpenQASM that are not enabled on the IBM QX, and thus are not covered in detail in this book. These include:
- Resetting a qubit
- if statements
- User-defined gates
- Built-in/physical/opaque gates
However, as some OpenQASM programs specified in the literature use these language features, and IBM QX may use them in the future, I will go over their syntax and usage briefly here.