#define is a useful C++ component that allows the programmer 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.
This can have some unwanted side effects though, if for example, a constant name that had been #defined is included in some other constant or variable name. In that case the text would be replaced by the #defined number (or text).
In general, the const keyword is preferred for defining constants and should be used instead of #define.
Syntax
#define constantName value
Note that the # is necessary.
Example Code
#define ledPin 3
// The compiler will replace any mention of ledPin with the value 3 at compile time.
Notes and Warnings
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.
We care about the privacy and personal data of our users.
To continue, please give us your consent:
Please confirm that you have read the privacy policy
Thank you for subscribing!
Curious to learn more?
Are you also a teacher, student, or professional that loves using Arduino in your day-to-day activities?
Then keep up-to-date with either our STEM or Professional monthly newsletters.
Arduino weekly newsletter (already subscribed)
Educators can benefit from the ever growing tech that shapes our environment through fun cool projects.
Why not awe your boss with highly innovative ways to help keep your enterprise connected at no extra cost?
Arduino Survey
We'd like to get to know you little better.
Please help us improve by answering this super short optional survey.
