You can wrap the assertion in `with_attr`, for example:


`with_attr error_message("My error message"):`


 `assert some_var = 0`


`end`


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

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?


My ABIs will be same right? In UI I am assuming I wont have to make any changes

Hello! This is day 8 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 “Field Elements”.  Perhaps you can help me?

```
// Unlike most systems where the primitive type is a 32 or 64-bit integer,
// the primitive type in Cairo is "felt", which stands for "field element".
// When we say "a field element" we mean an integer in the range -P / 2 < x < P / 2,
// where P is a very large (prime) number.
// Currently we use a 252-bit number (76 decimal digits).
// When we add, subtract or multiply and the result is outside the range above,
// there is an overflow.
//
// The most important difference between integers and field elements is division:
// Division of field elements (and therefore division in Cairo) is not the
// integer division you may be used to.
// In the next challenge, you'll see how to use unsigned_div_rem()
// for truncated (i.e., rounding down) integer division.
//
// Make the code below output the results of the following expressions:
// 1. 1 + 100, 1 - 100, 9 * 9.
// 2. pow(10, 74), pow(10, 75), pow(10, 76)
// 3. 12 / 3, (-12) / 3
// 4. 13 / 3 (This is an example of division in the field)

%builtins output

from starkware.cairo.common.serialize import serialize_word

// Computes base^exp.
func pow(base: felt, exp: felt) -> (res: felt) {
    if (exp == 0) {
        return (res=1);
    }

    let (res) = pow(base=base, exp=exp - 1);
    return (res=res * base);
}

func main{output_ptr: felt*}() {
    serialize_word(1 + 100);
    // Add your code here.

    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 make math operation with Field Elements (felts) in Cairo lang?

I am trying to deploy my contract using this tutorial
[https://medium.com/starknet-edu/deploying-to-starknet-with-the-universal-deployer-contract-c6de07092bfb](https://medium.com/starknet-edu/deploying-to-starknet-with-the-universal-deployer-contract-c6de07092bfb)
But as I follow the steps, I got an error at the contract declaration step: `Unitialized Contract`

Trying to deploy contract with Argent guide but got error Unitialized Contract

Hi, I was deploying contracts with `Contract.deploy`, but since the last version this method is gone :/

What should I do to deploy contracts now?

How to deploy a contract through starknet.py?

# Hello starknet fam!

I heard with the last release of protostar it is now possible to make multiple call to different contracts functions in one protostar invoke CLI.

Can someone show me a good exemple on how to use it?

Like multicall with approve and swap.

Thank you very much!

How to use multicall with protostar 0.9.0?

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?

Hey how can I get ETH for the test net in StarkNet?

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

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