该从该从哪里哪里开始开始学起学起呢呢？？PythonPython嘛嘛？？


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_This question was originally posted on [Triality](https://triality.org/question/479)_

开始学习Cairo

# Is Kakarot zkEVM a smart contract or a blockchain?

Is Kakarot zkEVM a smart contract or a blockchain?

What is the technical difference between Solidity -> Cairo transpiler and ZK-EVM Kakarot for StarkNet? Both of them interpret Solidity into Cairo and it can help Solidity developers to use StarkNet. 

But really, how does [Kakarot](https://github.com/sayajin-labs/kakarot) compare to [Nethermind's Warp](https://github.com/NethermindEth/warp)?

What is the technical difference of Kakarot compare to Nethermind's Warp?

Hey, I want to concatenate two arrays with known sizes in Cairo lang.
Is there any simple way how to do it? Can you share some of your code?

Is there any simple way to concat two arrays with known sizes in Cairo?

What libraries are secure to use in the Cairo language? How to know which library is audited? 

What libraries are secure to use in Cairo?

# Hello world!

I try to implement the function `abs_value` of the package `starkware.cairo.common.math` but i have this error

```
AssertionError: Expected main to contain the following arguments (in this order): ['range_check_ptr_ptr']. Found: ['range_check_ptr'].
```

I dont understand the error. 

Can someone explain the error to me, why it happens ? 

> I am doing the challenge #17daysOfCairo of the day 3


Full code

```
%builtins range_check_ptr
from starkware.cairo.common.math import abs_value

func main{range_check_ptr}() {
    let x = abs_value(-1);
    return ();
}
```


AssertionError with range_check_ptr_ptr

I’m signing a message using 
```
account.signMessage(data) 
```
and immediately verifying the signature with the same data and it’s returning false. I don’t see any issue open on this subject on starknet.js. Is this something you’ve already encountered by any chance?

here’s the code:

```python
const data = { types: proposeTypes, primaryType: 'Propose', domain, message };
const sig = await user.account.signMessage(data);
let res = await user.account.verifyMessage(data, sig); // returns `false`
```

I see that’s the expected way to use signMessage through the tests (https://github.com/0xs34n/starknet.js/blob/b20819424dea824c96ac31e0542733c84d87d441/__tests__/account.test.ts#L125-L126).

So I guess something’s going wrong when it comes to either hashing the data and signing it or hashing the data and verifying the signature?


btw: for those wondering: `verifyMessage` only works if the account is deployed: if you’re doing this with an account not deployed (basically just a keypair) then this won’t work :)

signing a message using account.signMessage(data) | starknet.js

Hey, is there a unsigned_div_rem supporting dividing by 2**128 ?

_This question was originally posted on [StarkNet Discord](https://www.newton.so/view?tags=discord)_

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