I have created a repository for the cairo challenge
https://github.com/chococrypto/17daysOfCairo

here is my answer

```
// Use the output builtin.
%builtins output

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

func print_hundredths{output_ptr: felt*}(max, init) {
    serialize_word(init);
    if(init == max) {
        return();
    }
    print_hundredths(max, init = init + 100);
    return();
}

func main{output_ptr: felt*}() {
    print_hundredths(400, 100);
    return ();
}
```


Can you help how to change the code so that it outputs 400 as well?

```
// The following code outputs the numbers 100, 200, 300.
// 1. Click on "Run" to see the output.
// 2. Change it to output 400 as well.

// Use the output builtin.
%builtins output

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

func main{output_ptr: felt*}() {
// Output 100 by calling serialize_word.
serialize_word(100);
// Output 200.
serialize_word(200);
// Output 300.
serialize_word(300);
// Return.
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-Playground-Newton-550dfcda6a2d449ca468be293c776578)*

How to make output like "hello world" in Cairo Language (StarkNet)?

repository challenge
https://github.com/chococrypto/17daysOfCairo

answer:


```
func add1(y:felt) -> (z:felt) {
    return (z=y + 1);
}

func add1_square(x: felt) -> (x: felt) {
    // Call `add1` and unpack the result into `z`.
    let (z) = add1(y=x);
    return (x=z * z);
}

func main() {
    // Call `add1_square` and save the result into `res`.
    let (res) = add1_square(x=12);

    // Verify the computation.
    assert res = (12 + 1) * (12 + 1);
    return ();
}
```


Hello! This is Day 2 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 “Functions”. Perhaps you can help me?

```python
// The following code is missing the function `add1`.
// 1. Click on "Run" to see the error.
// 2. Write the function `add1`, based on `add1_square`, so
//    that the program terminates successfully.
//
// Note that `add1` doesn't have to call other functions.
//
// You can learn more about functions [here](https://www.cairo-lang.org/docs/how_cairo_works/functions.html).

// Write your code here.

func add1_square(x: felt) -> (x: felt) {
    // Call `add1` and unpack the result into `z`.
    let (z) = add1(y=x);
    return (x=z * z);
}

func main() {
    // Call `add1_square` and save the result into `res`.
    let (res) = add1_square(x=12);

    // Verify the computation.
    assert res = (12 + 1) * (12 + 1);
    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 write a function in Cairo Lang (StarkNet)?

I wondered that such a basic function as `abs` should exist on cairo. Therefore, I went through [the cairo-lang repository](https://github.com/starkware-libs/cairo-lang/tree/master/src/starkware/cairo/common ) and found the function I wanted.

However, I had a problem with the implementation of the `abs` function. But thanks to the help from the cairo community I was able to solve it. Here is the [error](https://www.newton.wtf/view/6334a012acdf931bd1820924)

My answer for the day 3
```
%builtins range_check

from starkware.cairo.common.math import abs_value

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

func main{range_check_ptr}() {
    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 ();
}
```

[Repository challenge](https://github.com/chococrypto/17daysOfCairo)



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 ();
}
```

---


> 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 conditional expressions if..then..else in Cairo lang?

My answer with comments that may help to understand the execution of recursion


```
%builtins output

from starkware.cairo.common.serialize import serialize_word

func compute_sum{output_ptr: felt*}(n: felt) -> (sum: felt) {
    // serialize_word(n) -> print 10, 9, 8, 7, ... 0
    if (n == 0) {
        // When 0 is reached, return 0.
        return (sum=0);
    }
    let (sum) = compute_sum(n=n - 1);
    // serialize_word(n) -> print 1, 2, 3, 4, ... 10
    let new_sum = sum + n;
    serialize_word(new_sum); // --> print 1, 3, 6, ... 55
    return (sum=new_sum);
}

func main{output_ptr: felt*}() {
    let (res) = compute_sum(n=10);

    // Output the result.
    // serialize_word(res);
    return ();
}
```
[Repository challenge](https://github.com/chococrypto/17daysOfCairo)

Hello! This is day 7 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 “Recursion”.  Perhaps you can help me?

```
// The following code prints the sum of the numbers from 1 to 10.
// Modify the function `compute_sum` to print all the intermediate sums:
// 1, 1 + 2, 1 + 2 + 3, ..., 1 + 2 + ... + 10.
// Note: you'll have to add the implicit argument output_ptr to the
// declaration of compute_sum (in order to use the serialize_word function):
//   func compute_sum{output_ptr: felt*}(n: felt) -> (sum: felt)

// Use the output builtin.
%builtins output

from starkware.cairo.common.serialize import serialize_word

func compute_sum(n: felt) -> (sum: felt) {
    if (n == 0) {
        // When 0 is reached, return 0.
        return (sum=0);
    }

    // Otherwise, call `compute_sum` recursively to compute 1 + 2 + ... + (n-1).
    let (sum) = compute_sum(n=n - 1);
    // Add the new value `n` to the sum.
    let new_sum = sum + n;
    return (sum=new_sum);
}

func main{output_ptr: felt*}() {
    let (res) = compute_sum(n=10);

    // Output the result.
    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 make recursive function in Cairo Lang?

# Hello world!

I try to implement the function `abs_value` of the package `starkware.cairo.common.math` but i have this error

```
AssertionError: Expected main to contain the following arguments (in this order): ['range_check_ptr_ptr']. Found: ['range_check_ptr'].
```

I dont understand the error. 

Can someone explain the error to me, why it happens ? 

> I am doing the challenge #17daysOfCairo of the day 3


Full code

```
%builtins range_check_ptr
from starkware.cairo.common.math import abs_value

func main{range_check_ptr}() {
    let x = abs_value(-1);
    return ();
}
```


Popular tags

Profile

chocolaite

Wallet address: 0x901F89dA2f891109057e4695a576480e618B709b

Recent questions

Recent answers