LESSON 1

Writing Qubic Smart Contracts

Qubic contracts are written in a restricted C++ environment called the Qubic Programming Interface (QPI).

Key facts:

Deterministic & Secure

No dynamic memory, no pointers, fixed-size types only (e.g. uint8, uint16).

Single source file

All contract logic is self-contained and compiled to run natively on every validator (“Computor”).

Persistent State

Static variables become the contract’s on-chain state — up to 1 GiB.

Public Entry Points

Only methods registered in REGISTER_USER_FUNCTIONS_AND_PROCEDURES are callable externally.

CLI & Testnet

External data enters Qubic through Oracle Machines. These are deterministic feeders of real-world information — essential for contracts needing off-chain data.

Every contract must be deployed to Qubic testnet before submission to mainnet. This ensures validator and community testing before quorum voting.

Example (copied directly from QPI example repo):

void REGISTER_USER_FUNCTIONS_AND_PROCEDURES() {
    REGISTER_FUNCTION(greet);
    REGISTER_PROCEDURE(setGreeting)

PRO TIP

When planning your storage, think long term. Large state increases storage fees each epoch.

HANDS-ON TASK

Set up the Qubic Dev Kit and open the demo contract. Identify every variable that persists across ticks. Label which ones you’d keep if you were writing a simple token.

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HANDS-ON TASK

Set up the Qubic Dev Kit and open the demo contract. Identify every variable that persists across ticks. Label which ones you’d keep if you were writing a simple token.

PRO TIP

When planning your storage, think long term. Large state increases storage fees each epoch.

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