Value Types
uint, address, bool, bytes.
Value Types is a free Web3 & DApp Development Fundamentals lesson on CoddyKit — lesson 1 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Web3 & DApp Development Fundamentals learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
What Are Value Types?
Value types in Solidity hold their data directly and are copied whenever they are assigned to a variable or passed to a function.
This is different from reference types (arrays, structs, mappings) which point to a shared location. Value types include bool, integers, address, and fixed-size bytes.
- Always copied on assignment
- Stored compactly
- Predictable gas cost
Booleans
The bool type holds either true or false. It is the result of comparison and logical operators.
Solidity supports ! (not), && (and), || (or). Logical operators short-circuit, just like in most languages.
<code>bool isActive = true;
bool hasPaid = false;
bool ready = isActive && !hasPaid;</code>Unsigned Integers
uint stores non-negative whole numbers. uint is an alias for uint256.
You can choose smaller sizes in steps of 8 bits: uint8, uint16, ... up to uint256. Smaller types can save storage when packed together in a struct.
<code>uint256 balance = 1000;
uint8 smallCount = 255; // max value for uint8</code>Signed Integers
int stores values that can be negative or positive. int is an alias for int256.
An int8 ranges from -128 to 127. Use signed integers only when negatives are genuinely possible, since they are easy to misuse.
<code>int256 temperature = -15;
int8 delta = 100;</code>Overflow Protection
Since Solidity 0.8.0, arithmetic automatically reverts on overflow and underflow. You no longer need SafeMath for basic safety.
If you intentionally want wrapping behavior for gas savings, wrap the math in an unchecked block.
<code>uint8 x = 255;
// x + 1 would revert (overflow)
unchecked {
x = x + 1; // wraps to 0
}</code>The address Type
An address holds a 20-byte Ethereum account identifier. It can refer to a wallet (EOA) or a contract.
The address type exposes members like .balance (in wei) and methods such as .transfer() and .send().
<code>address owner = 0x5B38Da6a701c568545dCfcB03FcB875f56beddC4;
uint256 bal = owner.balance;</code>address vs address payable
A plain address cannot receive Ether directly. To send funds you need address payable, which adds .transfer() and .send().
You convert between them explicitly with payable(addr).
<code>address recipient = msg.sender;
address payable wallet = payable(recipient);
wallet.transfer(1 ether);</code>Fixed-Size Bytes
Solidity offers fixed-size byte arrays from bytes1 to bytes32. These are value types and are cheaper than dynamic bytes when the length is known.
They are useful for hashes, identifiers, and short fixed data.
<code>bytes32 hash = keccak256(abi.encodePacked('hello'));
bytes1 firstByte = hash[0];</code>Enums
An enum defines a custom type with a fixed set of named constants. Internally each value is a small uint starting at 0.
Enums make state machines readable, such as the status of an order.
<code>enum Status { Pending, Shipped, Delivered }
Status public current = Status.Pending;
function ship() public {
current = Status.Shipped;
}</code>Literals and Units
Solidity provides handy unit suffixes. Ether units: wei, gwei, ether. Time units: seconds, minutes, hours, days, weeks.
1 ether equals 10**18 wei.
<code>uint256 fee = 1 ether; // 1000000000000000000 wei
uint256 timeout = 2 days; // 172800 seconds</code>Default Values
Solidity has no null. Every value type has a zero default: uint is 0, bool is false, address is the zero address 0x0...0.
Checking against the zero address is a common guard.
<code>address public admin; // defaults to address(0)
function setAdmin(address a) public {
require(a != address(0), 'zero address');
admin = a;
}</code>Quick Check
Test your understanding of Solidity value types.
Recap
You learned the core value types in Solidity:
boolfor true/false logicuint/intwith built-in overflow protection since 0.8.0addressandaddress payablefor accounts and transfers- Fixed
bytesN,enum, and unit literals like1 ether
Remember: value types are copied, and every type has a zero default value.
Frequently asked questions
Is the “Value Types” lesson free?
Yes — the full text of “Value Types” is free to read here on the web, and the Web3 & DApp Development Fundamentals course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Web3 & DApp Development Fundamentals course, upgrade to CoddyKit PRO.
What will I learn in “Value Types”?
uint, address, bool, bytes. You practise Web3 & DApp Development Fundamentals with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start Web3 & DApp Development Fundamentals?
No prior experience is required. Web3 & DApp Development Fundamentals on CoddyKit is structured for beginners through advanced learners; this is — lesson 1 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “Value Types” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this Web3 & DApp Development Fundamentals lesson?
Yes. Every Web3 & DApp Development Fundamentals lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.