https://voyager.online/

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

Newton

Alternatively, you can use starkscan
https://starkscan.co/

Hello, anyone able to advise what the etherscan equivalent for starknet is ?

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

What the etherscan equivalent for starknet is ?

Hey guys, has anyone had `get_caller_address` problems in devnet ? I feel like it's returning address 0 when it shouldn't so I made this small contract to test it

```%lang starknet

from starkware.cairo.common.cairo_builtins import HashBuiltin

from starkware.starknet.common.syscalls import (get_caller_address)


func caller_addr() -> (res: felt) {
}



func fn_to_be_called{syscall_ptr: felt*, pedersen_ptr: HashBuiltin*, range_check_ptr: felt}() {
    let (caller) = get_caller_address();
    caller_addr.write(caller);    

    return ();
}


func get_caller_addr{syscall_ptr: felt*, pedersen_ptr: HashBuiltin*, range_check_ptr: felt}() -> (caller_addr: felt) {
    let (caller) = caller_addr.read();

    return (caller_addr=caller);
}```

and indeed `get_caller_addr` return address 0 after I called `fn_to_be_called` in the devnet. This is causing some problems in more complex contracts of course. Is it just me ?



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

Has anyone had `get_caller_address` problems in devnet ?

I have a question about how to print "Hello World" in Cairo 1. How do I log/print ?

How do I log/print in Cairo 1.0?

What are steps to create a new contract using starknetjs?

Does AA work on Mobile?

---

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Does Account Abstraction work on Mobile?

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! This is day 3 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 “Conditionals”. Perhaps you can help me?

```python
// The function `abs_eq` should return 1 if its inputs
// are equal or differ only in sign and 0 otherwise.
// Its current implementation is incorrect.
//
// 1. Click on "Run" to see where it fails.
// 2. Fix the body of `abs_eq`, so that the
//    program terminates successfully.

// Returns 1 if |x| = |y| (that is, x = y or x = -y),
// 0 otherwise.
func abs_eq(x: felt, y: felt) -> (bit: felt) {
    if (x == -y) {
        return (bit=1);
    } else {
        return (bit=0);
    }
}

func main() {
    let (bit) = abs_eq(2, -2);
    assert bit = 1;

    let (bit) = abs_eq(2, 3);
    assert bit = 0;

    let (bit) = abs_eq(2, 2);
    assert bit = 1;

    return ();
}
```

---


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How to make conditional expressions if..then..else in Cairo lang?

Are you able to nest mappings in Cairo like you can in Solidity?

e.g. in Solidity you can do
```solidity
mapping(address => mapping(uint256 => bool));
```
is this doable in Cairo? I want to do something similar to

```cairo

func mappingA(value: felt) -> func mappingB(value: felt)  -> (value: felt){
}
```

mapping(x, y) -> (z) is not gonna work, here is some context:

I'm working through the sample ERC721_Metadata.cairo and ERC721_Metadata_Base contract shown here https://github.com/starknet-edu/starknet-erc721/tree/main/contracts/token/ERC721

It looks like from what I can tell the tokenUri is set for each domain, and even though calling the @view function does take in a tokenId, calling to set the tokenUri does not and it's not clear to me how that mapping could exist otherwise. So I wanted to modify the contract to have a token_id -> token_uri mapping. Because of the way those mappings exist though, you need to provide both the token_uri_len: felt and token_uri: felt*  when writing them. This means it can only be done once, otherwise you'd need a specific @storage_var for every token that's minted, just to hold it's tokenuri. I was hoping to do something like 

```cairo
// Represents a tokenUri
struct TokenUri {
    // The length of the token bytes
    token_uri_len: felt,
    // The pointer to the beginning of the token uri bytes
    token_uri: felt*,
}

@storage_var
func token_uris(token_id: felt) -> (token_uri: TokenUri) {
}
```


But because of the token_url: felt*  pointer in that struct, it can't be used as a storage variable return type. It gives an error when I try to compile showing
```cairo
starknet_contracts/ERC721_Metadata.cairo:29:36: The return type of storage variables must be a felts-only type (cannot contain pointers).
func token_uris(token_id: felt) -> (token_uri: TokenUri) {
```

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

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What the etherscan equivalent for starknet is ?

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