29
votes
Accepted
Why write uint256 instead of uint if they're the same thing?
Yes, they are exact aliases.
Some developers (including me) prefer to use uint256 because it is consistent with other uint data types, which also specify their size, and also because making the size ...
- 16.9k
19
votes
Max/min values of standard data types
I assume you mean the integer types, because those are really the only types in Solidity that have a maximum and a minimum.
Solidity does not support floating point types, and most likely will never ...
- 10.5k
13
votes
Accepted
Max/min values of standard data types
Updated 2020
Solidity 0.6.8 introduced min and max keywords that can now natively tell you the min and max of an expected type. From the release page:
Implemented type(T).min and type(T).max for ...
- 18.3k
10
votes
Why write uint256 instead of uint if they're the same thing?
In addition to what @EdmundEdgar said, it's also better to be explicit when constructing method signature ID's.
For example if doing bytes4(keccak('transfer(address, uint)')), you'll get a different ...
- 5,233
8
votes
Accepted
Can solidity have negative numbers?
The answer to your question is Yes:
Solidity supports int types, which are treated arithmetically as signed values (i.e., can be positive, negative and zero).
The answer to your concern is No:
...
- 26.2k
6
votes
Accepted
Convert number to bytes in ethersjs?
ethers also has a padding function where it will add the zeros to make it the correct length. It looks like this
const oracleResponse = ethers.utils.hexZeroPad(ethers.utils.hexlify(1), 32)
This will ...
- 12.5k
5
votes
Accepted
Why do reputable ERC721 contracts use uint256 so often?
Edited Answer
The reason people like using uint256 for most calculation is that OpenZeppelin has a SafeMath library for uint256 that prevent number overflow for sol version < 0.8.
Additional ...
- 653
4
votes
Accepted
How to take the average of two uint256s without overflowing?
After posting the question, I realised I gave the answer myself.
I simply have to check if both x and y are odd numbers and, if yes, add 1 to the result:
function avg(uint256 x, uint256 y) external ...
- 18.9k
4
votes
Accepted
Why Ethereum sets user balance to MaxBig256 whenever a contract query is performed?
In Ethereum, to execute operation in EVM costs you gas. One can change any state in the blockchain which is done through making transaction. In this case, you will be charged ether. To make ...
4
votes
Accepted
Why does uint 0 - 20 not cause an underflow?
That's because since solidity 0.8.0 the overflow / underflow are automatically checked :
"Arithmetic operations revert on underflow and overflow. You can use unchecked { ... } to use the previous ...
- 7,901
4
votes
Why uint8 for decimals in ERC20 tokens?
Well, nothing will mess up if you use uint8 for token decimal.
The reason why most of the ERC20 smart contracts use uint8 for the decimal is that because the EIP-20 propose to use uint8 for decimals.
...
- 397
3
votes
Accepted
How to set multiple unit64 values in a uint256 variable
Your smart contract code is okay, but this is probably simpler:
pragma solidity 0.5.7;
contract Uncombine {
function getVariables(uint256 combined) external pure returns (uint64 variable1, ...
- 28.1k
3
votes
Accepted
Is it better practice to use smaller uint sizes when applicable?
It really depends on the way you implement it. EVM allocates you new memory slots in 256 bit chunks and in order that the state variables are declared.
So if you declare them like that:
uint32 time;
...
- 1,014
3
votes
Accepted
Does casting a Keccak256 hash to a uint256 increase likelihood of a collision?
A keccak256 string has a length of 256 bits. Obviously, uin256 also has 256 bits. Since they both have the same length, there shouldn't be any problems when converting them even back and forth.
I ...
- 30.4k
2
votes
Why write uint256 instead of uint if they're the same thing?
I hate to say RTFM, but this one was too trivial. "uint and int are aliases for uint256 and int256, respectively." --https://solidity.readthedocs.io/en/v0.4.21/types.html#value-types
- 279
2
votes
Accepted
Ethers.js invalid number value while deploying contract
const tokenWeiPrice = (answers.priceEur / ethEur) * Math.pow(10, 18);
Problem #1: 10 ^ 18 > Number.MAX_SAFE_INTEGER
Problem #2: tokenWeiPrice is not necessarily an integer.
You should use ...
- 26.2k
2
votes
Accepted
bytes32/uint256 conversion
Assuming
genes.test.call(0x000063169218f348dc640d171b000208934b5a90189038cb3084624a50f7316c)
is JavaScript, your problem is probably that the parameter is getting interpreted as a JavaScript number,...
- 16.9k
2
votes
Accepted
Solidity. Return a Sruct that lives inside an array
You forgot to name your variable. You only gave it a type. Try this:
function getStudent(uint id) ... {
return (students[id].name, students[id].ethAddress, ...);
}
- 28.1k
2
votes
Solidity - preventing negative uint parameters/overflow
Since web3 apparently doesn't require functions with uint parameters to have positive values
Not true. uint is always a positive number, by definition.
I suspect the issue is about how the contract ...
- 55.6k
2
votes
Accepted
Mapping with iterating uint as identifier - multiple transactions in the same block
No, it doesn't matter whether transactions are in the same block or not. Each transaction is processed on its own, sequentially. The code you propose is fine, though an array may make more sense.
- 28.1k
2
votes
Passing '-1' to a solidity function which takes a 'uint256' argument as input
I'm unsure if web3 truffle do some magic of their own but I'd guess no, because they don't need to interpret the values themselves. Anyway, if you test this in Remix you will also see that it wraps ...
- 30.4k
2
votes
converting uint256 to string
oraclize helped
pragma solidity ^0.5.3;
uint public degrees= 40;
function getString() public view returns(string memory){
string memory a = "today is ";
...
- 35
2
votes
Accepted
variable declared as uint but accepting negative values instead of throwing errors
Both, uint and int are 256-bit long in Solidity, so arbitrary sequence of 256 bits may be interpreted in both ways. For example, sequence of 256 "ones" is -1 when interpreted as int, and is ...
- 7,373
2
votes
Accepted
How to get the first digit of a uint256
Substitute x for whichever number you want to check for.
function highestOrderDigitIsX(uint256 number, uint256 x) public pure returns (bool) {
while (number >= 10) {
number /= 10;
}...
- 38k
2
votes
Accepted
How to add three numbers using safemath?
Writing 5.add(7) is a syntax sugar for add(5, 7).
So first expression 5.add(7.add(8)) is add(5, add(7, 8)) and the second one 5.add(7).add(8) is add(add(5, 7), 8).
In the particular case of SafeMath's ...
- 30.2k
2
votes
Updating values that are packed inside a uint256
To make this a bit easier to visualize, let's say you have four numbers and each takes 2 bits. 8 bits in total.
Your 8 bit integer might look for example like this: 10 10 11 01. In decimal, the ...
- 30.4k
2
votes
Accepted
How can we assign bytes to uint256 variables in solidity?
You can assign smaller integers to larger ones.
A byte is uint8. Not semantically, but from the bits points of view.
- 22.2k
1
vote
Accepted
How to send uint256 and Address types to Smart contract in JavaScript web3/ethers?
It seems like you are trying to use the wrong getAmountsOut function:
// performs chained getAmountOut calculations on any number of pairs
function getAmountsOut(address factory, uint amountIn, ...
- 410
1
vote
Accepted
Error: overflow
JavaScript can natively only deal with integers of size 2^53 - 1. So to deal with the big numbers in Solidity, you can use the BigNumber library. Assuming you're using truffle's test suite, that would ...
- 478
1
vote
compare uint from datestamp always return true
There are a few issues with your code.
You should always use BigNumber when using integers. JavaScript can't handle big numbers. Even if you know the numbers will never be too big, in my opinion it's ...
- 30.4k
Only top scored, non community-wiki answers of a minimum length are eligible