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## Define

`#define` is a useful C component that allows you to give a name to a constant value before the program is compiled. Defined constants in arduino don't take up any program memory space on the chip. The compiler will replace references to these constants with the defined value at compile time.

Arduino defines have the same syntax as C defines:

#### Syntax

`#define constantName value`

Note that the # is necessary.

#### Example

    #define ledPin 3
    // The compiler will replace any mention of ledPin with the value 3 at compile time.

#### Tip

There is no semicolon after the #define statement. If you include one, the compiler will throw cryptic errors further down the page.

    #define ledPin 3;    // this is an error

Similarly, including an equal sign after the #define statement will also generate a cryptic compiler error further down the page.

    #define ledPin  = 3  // this is also an error

#### See

- Constants

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