That's actually a nice question!
In your example, the compiler is not able to compute the change of ap, and here's why "x" is alternating between 1 and 2

You can see [a similar question](https://www.newton.so/view/63372c85f20834f8447ac533) there it is explained a bit more clearly explained what is a revoked reference.

## About revoked references
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.

When you write "let" you do not create a variable, instead you create a reference to the memory slot.
I may even cause an error, for example:

```cairo
 let (x) = foo(1);
 let (y) = foo(2);
 serialize_word(x + y);
```
will cause an error:

```cairo
Error: code:43:20: Reference 'x' was revoked.
    serialize_word(x + y);
                   ^
Reference was defined here:
code:41:10
    let (x) = foo(1);
         ^
```


vargastartup

I am currently running this code

```
func main() {

    let x = [ap];
    [ap] = 1, ap++;

    [ap] = 2, ap++;

    [ap] = x, ap++;
    jmp rel -1;  // Jump to the previous instruction.
}

And what is happening is that "x" is alternating between 1 and 2 and I couldn't figure out why.

Also, it wasn't very clear to me what a "Revoked Reference" means. Is it when you cannot access a certain [ap] when running a specific function?

This is the link to the exercise:
https://www.cairo-lang.org/docs/how_cairo_works/consts.html#revoked-references

Revoked References exercise from Cairo-lang

How can I send a Uint256 amount of ERC20 tokens from L1 to starknet?
I have "amount" as a uint256 on L1 but how should I build my payload for "`sendMessageToL2`" to match the Uint256 format of Cairo?

---

This question is participating in [Newton Bounties | Incentivized Test Program](https://www.notion.so/Newton-Bounties-Incentivized-Test-Program-94322ad48e7d40a3adcf36f6b26174cd) Every verified valid question gets $10 USDC (mainnet)

How can I send a Uint256 amount of ERC20 tokens from L1 to starknet? And how should I build my payload for "sendMessageToL2" to match the Uint256 format of Cairo?

I used the Nethermind Warp Traspiler to translate the Solidity to Cairo successfully, but there was a problem with the test. I don't think there is this `warplib` package, `node_module` there is, but there is no python package. How do I generate python packages?


```python
from warplib.memory import wm_new
from warplib.maths.utils import felt_to_uint256
```

### How to represent / my environment
I used python virtual environment to develop cairo, and then I used this tool to convert solidity to cairo. After compiling, I reported an error and saw that `the warp-related package was not found`.

Warp Traspiler error: the warp-related package was not found. How do I generate python packages?

Hey folks, do you know how I could read a felt* from ap?

I want to do something like this:

```rs
    let (hello : felt*) = alloc();
    tempvar world : felt* = hello;
    let world_like : felt* = [ap-1];
```

when I do tempvar world = hello, I ensure I add hello (the pointer) to [ap] and then I increase ap so world_like = [ap-1] should be the same thing than world

But I get this error:

```
Cannot assign an expression of type 'felt' to a reference of type 'felt*'.
    let world_like : felt* = [ap-1];
```

When doing a similar code:

```rust
        let (func_pc: felt*) = get_label_location(storage_var);
        _prepare_call(pedersen_ptr, range_check_ptr, len_inputs, inputs + len_inputs);
        call abs ap[11 - 6 * 2];
```

I get ```
Cannot apply subscript-operator to non-pointer, non-tuple type 'felt'.
        call abs ap[11 - 6 * 2];  // removing alloc_locals by calling ap[11-6*2] ?
```

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

how I could read a felt* from ap in Cairo lang?

How do I connect my DAPP to a Starknet node using starknetjs?

How can I test on multi-chain with both Starknet and Ethereum?


ApeWorX: How can I test on multi-chain with both Starknet and Ethereum?

Hello guys, I would like to know if CAIRO work in python3.10 venv? Because I have a problem to install python 3.9.


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

Does Cairo work in python3.10 venv? I can’t install python 3.9

Hi, I'm trying to solve a Playground exercise on the [Cairo website](https://www.cairo-lang.org/playground/) named "Conditionals". I don't know how to make OR operator in Cairo. I tried something like that:

```
func abs_eq(x: felt, y: felt) -> (bit: felt) {
    if (x == -y) or (x == y) {
        return (bit=1);
    } else {
        return (bit=0);
    }
}
```

but it gives me an error


`Error: code:12:18: Unexpected token Token('IDENTIFIER', 'or'). Expected: "{".
    if (x == -y) or (x == y) {`

How can I solve it?


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Revoked References exercise from Cairo-lang

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