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Your latest solution is wrong and is impossible to submit. Note that you do not need to change the function signature provided. Also, read this for info on how to train on Codewars

Hi, I completed a task as required, and they published my result with no error. but I did not see any earnig of honors for it and I did not see in my profile that task is completed. Under completed task it still remains zero. What is the reason for this?

The ISSUE label is for provable kata issues. Please use the QUESTION label when asking a question and appropriate formatting when posting code. See https://docs.codewars.com/training/troubleshooting#post-discourse.

You don't need to do IO on codewars. See https://docs.codewars.com/training/troubleshooting/#.print-vs-return and https://docs.codewars.com/training/training-example/#writing-a-solution.

If your code is rejected, it's because your code doesn't do what it is asked. It's as simple as that.

See https://docs.codewars.com/training/training-example.

Why does codewars gives us a preset of code that we should use instead of us choosing our method?

If you don't keep the data types and the method's name, then it won't work. The tests look for that. Normally initial code shouldn't make it more difficult for you. If you write your code in your IDE from scratch, then you have the extra work to adapt it to the initial code here.

Not a kata issue, please use the initial code and write your code inside it.

/* d - the days to rent */
unsigned rental_car_cost(unsigned d)
{
    return 0u;
}

Also, the input value is passed as the argument of that function, not read from the keyboard. Please read this: https://docs.codewars.com/getting-started/solving-kata