An account contract (what you call an abstract account) is a smart contract that is able to manipulate assets.

Since it's a smart contract, it's address is derived from it's code.

The logic around user authentication is entirely left to the account contract developer. It can be by using private/public keys, derived from a seed; or from any other means deemed appropriate.

What is an abstract account? Where is the account address derived from? Does the account address also come from the mnemonic and private key?

Newton

What is an abstract account? For example: StarkNet Account Abstraction

does cross-chain bridge produce its own block? or it only verify the blocks from A/B chain?

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

Does cross-chain bridge produce its own block? Or it only verify the blocks from A/B chain?

In solidity I can add an error message as the 2nd argument to require, like: `require(<some_condition>, "My error message");`


Is there an equivalent way to do this in a starknet contract? Like for `assert some_var = 0`


ㅤ
_This question was originally posted on [Triality](https://triality.org/question/795)_

Cairo: How do I write a custom error message when an assert fails?

### *From Newton AI*
*"Assembly" is a low-level language that is used to write smart contracts for the Ethereum Virtual Machine (EVM). It is similar to machine code, which is the code that is run directly on a computer's central processing unit (CPU). Assembly is often used in Solidity contracts to perform complex tasks or to optimize the performance of the contract.*

*If a Solidity contract contains assembly code, it is important to be careful when working with it, as it can be difficult to read and understand. Additionally, certain assembly instructions, known as "special EVM calls," can have unintended consequences if not used correctly. For example, some special EVM calls can cause a contract to consume an excessive amount of gas, which can make it more expensive for users to interact with the contract.*

*It is generally recommended to avoid using assembly in Solidity contracts if possible, as it can make the contract more difficult to understand and maintain. If you do need to use assembly, it is important to thoroughly test and debug the contract to ensure that it functions as intended.*

What if my solidity contract contains Assembly or special EVM calls ?

Hello! This is day 14 of the 17 days of the Cairo Challenge. And I have no idea how to solve the [playground](https://www.cairo-lang.org/playground/) exercise “Hints”.  Perhaps you can help me?

```
// The following function uses hints to efficiently compute the square root `res`
// of the argument `n`.
// The idea is that the verifier only needs to be convinced that res * res = n,
// it doesn't really care how res was computed.
// In such cases, we don't have to compute res in pure Cairo - we can write a
// piece of Python code inside the Cairo program, which is called a "hint".
// A hint is a piece of code that the prover runs to initialize
// some memory cells. Note that it is completely transparent from the verifier's
// point of view, so the result of the hint *must* be verified using pure Cairo
// instructions (e.g., the "assert n = res * res" instruction below).
//
// 1. Comment out the line "assert n = res * res;" and run the code. Does it still output
//    the expected value? Can you explain why the assert is nonetheless essential?
//    Hint: Recall that from the verifier's point of view, the hint does not exist.
// 2. Uncomment the assert line and change the function to compute the fourth
//    root.

%builtins output

from starkware.cairo.common.serialize import serialize_word

// Computes the square root (over the integers) of `n`.
// Prover assumption: The square root exists.
func sqrt(n) -> (res: felt) {
    alloc_locals;
    local res;

    // Set the value of res using a Python hint.
    %{
        import math

        # Use the ids variable to access the value of a Cairo variable.
        ids.res = int(math.sqrt(ids.n))
    %}

    // From the verifier's point of view, the hint is completely transparent.
    // The following line guarantees that `res` is the square root
    // (either the positive or negative) of `n`.
    assert n = res * res;
    return (res=res);
}

func main{output_ptr: felt*}() {
    let (res) = sqrt(256);
    serialize_word(res);
    return ();
}
```

---

> Answers to this question are a part of the ✨ 17 days of Cairo Lang with Playground & Newton. ✨
> 

*Vote for your favorite answer - the best answer will win a $10 award. A new day – a new reward! During the next 17 days, our goal is to attract more developers to the Cairo language and to systematize the knowledge of Cairo lang. [Read rules](https://www.notion.so/17-days-of-Cairo-Lang-with-Newton-550dfcda6a2d449ca468be293c776578)*

How to use Hints in Cairo Lang?

Does anyone know how to print a uint256 in protostar tests?

```
let (local balance) = IERC20.balanceOf(asset, owner);
%{
    balance = reflect.balance.get()
    print("current owner balance: ", balance)
%}
```

this errors out: [https://github.com/software-mansion/protostar/issues/1129](https://github.com/software-mansion/protostar/issues/1129)

Does anyone know how to print a uint256 in protostar tests?

Hi,

any idea what this could be caused by? This function is mentioned only once in the whole codebase. I’m trying to do protostar build

```python
Redefinition of '__wrappers__.get_pool_balance.__wrapped_func'.

func get_pool_balance{syscall_ptr : felt*, pedersen_ptr : HashBuiltin*, range_check_ptr}(
```

This error always appears with the first function it encounters that is annotated with either @view or @external

Can be reproduced in the repro-redefinition branch of [https://github.com/CarmineOptions/carmine-protocol.git](https://github.com/CarmineOptions/carmine-protocol.git)

Has anyone seen this error in proto? Redefinition of *`wrappers.*ourfunctionname.__wrapped_func__’`?

Any idea what this could be caused by?

>Hello! This is day 5 of the 17 days of the Cairo Challenge. And I have no idea how to solve the [playground](https://www.cairo-lang.org/playground/) exercise “Revoked references”. Can you run these 6 steps and write down what you see?

```
// The scope of some types of references in Cairo (e.g., return values of
// functions and temporary variables) is somewhat restricted.
// For example, a call to another function may revoke those references.
//
// 1. Try to run the following code. You should get an error that `x` was revoked
//    (this is because of the second call to `foo`).
// 2. In simple cases, like this one, the compiler can solve this automatically
//    if the "alloc_locals" keyword is used within the function's scope.
//    Add "alloc_locals;" to the beginning of main(), and make sure the code works.
// 3. To understand what happens behind the scenes, replace "alloc_locals;" with
//    "ap += SIZEOF_LOCALS;" - this command allocates memory cells for local variables
//    (you'll need them below) but doesn't enable the mechanism that
//    automatically resolves revoked references.
//    Trying to run the code now should result in the original error.
// 4. Solve the problem manually by copying the value of `x` to a local variable
//    (e.g., "local x2 = x;"). Local variables are not revoked when functions
//    are called.
//    You can read more about local variables [here](https://www.cairo-lang.org/docs/how_cairo_works/consts.html#local-vars).
// 5. You can even use the same name: "local x = x;".
//    This is called "reference rebinding", where the meaning of `x` changes:
//      Before this line, `x` refers to the return value.
//      After that, `x` refers to the local variable.
// 6. A shorter syntax is "let (local x) = foo(10);" which achieves the same goal.
//    Try it!

%builtins output

from starkware.cairo.common.serialize import serialize_word

// Returns a^3 for a != 0 and 1 otherwise.
func foo(a) -> (res: felt) {
    if (a == 0) {
        return (res=1);
    } else {
        return (res=a * a * a);
    }
}

// Outputs the value 10^3 + 5^3.
func main{output_ptr: felt*}() {
    let (x) = foo(10);
    let (y) = foo(5);
    serialize_word(x + y);
    return ();
}
```

---

> Answers to this question are a part of the ✨ 17 days of Cairo Lang with Playground & Newton. ✨
> 

*Vote for your favorite answer - the best answer will win a $10 award. A new day – a new reward! During the next 17 days, our goal is to attract more developers to the Cairo language and to systematize the knowledge of Cairo lang. [Read rules](https://www.notion.so/17-days-of-Cairo-Lang-with-Newton-550dfcda6a2d449ca468be293c776578)*



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What is an abstract account? For example: StarkNet Account Abstraction

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