Understanding Smart Contract working in etherium

Source: Dev.to

Introduction

Solidity is a programming language designed for writing smart contracts on the Ethereum blockchain. Smart contracts are self‑executing programs that contain a predefined set of rules, conditions, and functions. Once deployed to the blockchain, they run automatically when specific conditions are met—without the need for intermediaries.

Smart contracts run on the Ethereum Virtual Machine (EVM), a decentralized runtime environment that ensures the same code executes identically on every Ethereum node. These contracts handle transactions, store data, and interact with other contracts based on their programmed logic.

How Are Smart Contracts Triggered?

Smart contracts do not run on their own; they execute only when triggered by a transaction. A contract can be triggered when:

• A user sends a transaction.
• Another smart contract calls it.
• An external application (dApp backend, script, or bot) interacts with it.

In all cases, execution starts with a transaction sent to the contract address.

Example: Triggering a Smart Contract Using MetaMask

1. User initiates a transaction in MetaMask.
2. MetaMask prepares the transaction with the following details:
   • Contract address – which smart contract to call
   • Function selector – which function to execute
   • Parameters – input values required by the function
   • Gas limit & gas price – how much the user is willing to pay for execution
   • Value (optional) – amount of ETH (or native coin) to send

Transaction Creation and Signing

• The user reviews and signs the transaction in MetaMask.
• The signed transaction is broadcast to the network.

Block Validation and Execution

• Validators (miners or validators) include the transaction in a block.
• The EVM executes the contract code as part of block validation.

What Happens Inside the EVM?

1. Locate the contract code at the specified address.
2. Execute the function logic with the provided parameters.
3. Check conditions (e.g., balances, require statements).
4. If any check fails, the transaction reverts and all state changes are discarded (gas is still consumed).

Token Standards and Protocols

Common token standards (e.g., ERC‑20, ERC‑721) define how functions like transfer, approve, and balanceOf behave, ensuring compatibility across wallets and dApps.

Summary

• Smart contracts execute only when triggered by a transaction.
• Wallets like MetaMask prepare and sign those transactions.
• Validators execute the contract code inside the EVM.
• Execution follows strict rules, consumes gas, and the result is permanently recorded on the blockchain.