You are attempting to access an index in the array that is out of bounds. Make sure that `index` is within the bounds of the array (between 0 and `arr` length - 1)


ㅤ
_This answer was originally posted on [Triality](https://triality.org/question/606)_

I am trying to index into an array in cairo, and getting the following error:


`Unknown value for memory cell at address 13:2`


The line of code throwing the error is:


`let item = arr[index]`


ㅤ
_This question was originally posted on [Triality](https://triality.org/question/606)_

Cairo: Unknown value for memory cell at address

Hey, I'm using StartkNet.py to make a transaction and it gets rejected. 
How to solve it?

What does this error means? (AssertionError: assert_not_zero failed: 0 = 0.)

Just saw this in Cairo v0.10 docs: "support using functions as expressions"
Can anyone explain how does that work exactly? any example would be very helpful
It's mentioned here: https://github.com/starkware-libs/cairo-lang/releases/tag/v0.10.0#:~:text=Support%20using%20functions%20as%20expressions

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

Can you explain Cairo v0.10 usage functions as expressions?

What’s the difference between Account Abstraction (AA) and Externally Owned Accounts (EOA)?

---

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What’s the difference between Account Abstraction (AA) and Externally Owned Accounts (EOA)?

When using the command `ape starknet accounts list` will this show all my accounts on both starknet testnet and mainnet? 


ApeWorX: Using ape starknet accounts list 

Why will I use events in the Cairo language? Can I use it on a front-end client application side?

Why will I use events in Cairo language?

Hello! This is day 4 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 “Variables”. Can you launch this code with the instructions and write down how many steps the program has in the output?

[BONUS]: try to make it faster

```
// The following code outputs the 9th power of 2.
// 1. Click on "Debug" to run the code, and then click on
//    the arrows in the memory panel to trace the program
//    step by step.
//
// Observe that the computation of `z` take 8 steps and
// creates 8 temporary variables. This is because `let`
// simply replaces each instance of `y` with `x * x * x`
// and each instance of `z` with `y * y * y`, which is
// expanded to nine multiplications.
//
// 2. Change the two `let`s to `tempvar`s and run the program.
//
// "tempvar" stands for "temporary variable", which means that
// a variable will be allocated for the intermediate values
// (`x * x * x` and `y * y * y`). This reduces the same
// computation to use only 4 steps and 2 new variables.
//
// 3. Replace all three instance of the keyword `tempvar`
//    with `local`, uncomment the line containing `alloc_locals`
//    and run the code again.
//
// The behavior of the code doesn't change. This is because
// the keyword `local` allocates a new variables for the
// intermediate values as well. The main difference between
// `local` and `tempvar` is explained in the next challenge.

// Use the output builtin.
%builtins output

// Import the serialize_word() function.
from starkware.cairo.common.serialize import serialize_word

// Outputs the value 2^9.
func main{output_ptr: felt*}() {
    // alloc_locals;
    tempvar x = 2;
    let y = x * x * x;
    let z = y * y * y;
    // Because of the `let`s, the following line is equivalent to
    // serialize_word(x * x * x * x * x * x * x * x * x).
    serialize_word(z);
    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)*

What is the difference between tempvar/let in Cairo Lang? How to use allow_locals and local?

is there anything wrong with the testnet? why is it so slow now?

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

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