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13. Data Variables (define-data-var)

Single mutable storage variables.

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Data variables store a single value in contract storage, updated with `var-set` and accessed with `var-get`.

clarity
(define-data-var counter uint u0)
(var-set counter (+ (var-get counter) u1))

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  1. 1. Which function updates a data variable?

  2. 2. Which function reads a data variable?

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