Solidity by Example
version 0.7.6


How much ether do you need to pay for a transaction?

You pay gas spent * gas price amount of ether, where

  • gas is a unit of computation
  • gas spent is the total amount of gas used in a transaction
  • gas price is how much ether you are willing to pay per gas

Transactions with higher gas price have higher priority to be included in a block.

Unspent gas will be refunded.

Gas Limit

There are 2 upper bounds to the amount of gas you can spend

  • gas limit (max amount of gas your willing to use for your transaction, set by you)
  • block gas limit (max amount of gas allowed in a block, set by the network)
// SPDX-License-Identifier: MIT
pragma solidity ^0.7.6;

contract Gas {
    uint public i = 0;

    // Using up all of the gas that you send causes your transaction to fail.
    // State changes are undone.
    // Gas spent are not refunded.
    function forever() public {
        // Here we run a loop until all of the gas are spent
        // and the transaction fails
        while(true) {
            i += 1;

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