## 21 Type Qualifiers ¶

A declaration can include type qualifiers to advise the compiler about how the variable will be used. There are three different qualifiers, `const`, `volatile` and `restrict`. They pertain to different issues, so you can use more than one together. For instance, `const volatile` describes a value that the program is not allowed to change, but might have a different value each time the program examines it. (This might perhaps be a special hardware register, or part of shared memory.)

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