> For the complete documentation index, see [llms.txt](https://www.ankitavirani.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://www.ankitavirani.com/experience/protocols/ercs-and-eips/erc-20.md).

# ERC-20

## ERC-20: Fungible Token Standard 💰

ERC-20 is the most widely used token standard in the Ethereum ecosystem. It was introduced to create a common set of rules for fungible tokens, enabling seamless exchange and interoperability.

Key functions of ERC-20:

* totalSupply(): Returns the total token supply
* balanceOf(address account): Returns the token balance of a given address
* transfer(address recipient, uint256 amount): Transfers tokens to a specified address
* approve(address spender, uint256 amount): Allows a spender to withdraw tokens from your account
* transferFrom(address sender, address recipient, uint256 amount): Transfers tokens from one address to another

Example ERC-20 implementation:

```solidity
pragma solidity ^0.8.0;

contract ERC20Token {
    string public name;
    string public symbol;
    uint8 public decimals;
    uint256 private _totalSupply;
    mapping(address => uint256) private _balances;
    mapping(address => mapping(address => uint256)) private _allowances;

    event Transfer(address indexed from, address indexed to, uint256 value);
    event Approval(address indexed owner, address indexed spender, uint256 value);

    constructor(string memory _name, string memory _symbol, uint8 _decimals, uint256 initialSupply) {
        name = _name;
        symbol = _symbol;
        decimals = _decimals;
        _totalSupply = initialSupply * 10**uint256(decimals);
        _balances[msg.sender] = _totalSupply;
        emit Transfer(address(0), msg.sender, _totalSupply);
    }

    function totalSupply() public view returns (uint256) {
        return _totalSupply;
    }

    function balanceOf(address account) public view returns (uint256) {
        return _balances[account];
    }

    function transfer(address recipient, uint256 amount) public returns (bool) {
        _transfer(msg.sender, recipient, amount);
        return true;
    }

    function approve(address spender, uint256 amount) public returns (bool) {
        _approve(msg.sender, spender, amount);
        return true;
    }

    function transferFrom(address sender, address recipient, uint256 amount) public returns (bool) {
        _transfer(sender, recipient, amount);
        uint256 currentAllowance = _allowances[sender][msg.sender];
        require(currentAllowance >= amount, "ERC20: transfer amount exceeds allowance");
        unchecked {
            _approve(sender, msg.sender, currentAllowance - amount);
        }
        return true;
    }

    function _transfer(address sender, address recipient, uint256 amount) internal {
        require(sender != address(0), "ERC20: transfer from the zero address");
        require(recipient != address(0), "ERC20: transfer to the zero address");
        uint256 senderBalance = _balances[sender];
        require(senderBalance >= amount, "ERC20: transfer amount exceeds balance");
        unchecked {
            _balances[sender] = senderBalance - amount;
        }
        _balances[recipient] += amount;
        emit Transfer(sender, recipient, amount);
    }

    function _approve(address owner, address spender, uint256 amount) internal {
        require(owner != address(0), "ERC20: approve from the zero address");
        require(spender != address(0), "ERC20: approve to the zero address");
        _allowances[owner][spender] = amount;
        emit Approval(owner, spender, amount);
    }
}
```


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