Counter

counter.clar

;; An on-chain counter that stores a count for each individual

;; Define a map data structure
(define-map counters
  principal
  uint
)

;; Function to retrieve the count for a given individual
(define-read-only (get-count (who principal))
  (default-to u0 (map-get? counters who))
)

;; Function to increment the count for the caller
(define-public (count-up)
  (ok (map-set counters tx-sender (+ (get-count tx-sender) u1)))
)

Contract Summary

The Counter contract is a simple on-chain counter that maintains individual count values for each principal address. This minimalist contract demonstrates fundamental Clarity data structures and state management patterns.

What this contract does:

• Stores a separate counter value for each user (principal)

• Provides read-only access to retrieve any user's count

• Allows users to increment their own counter by 1

• Initializes counters at 0 for new users automatically

What developers can learn:

• How to use define-map to create key-value storage in Clarity

• Pattern for per-user state management using principal addresses

• Using default-to to handle missing map entries gracefully

• Simple read-only vs public function distinction

• Basic arithmetic operations and map updates with map-set

• The tx-sender context variable for identifying callers