c Functional problem of calculating the length of an array using language sizeof operation

Hello, everyone I am a student studying C language.

While solving the problem of creating a function that sorts the integers of an array in descending order, obtaining the length of the array from a function other than the main function results in a fixed value of 1.

I once heard that finding the length of an array with a size of operator is not good for other functions, so I looked through the book, but I can't see the contents. I'm asking because I can't know exactly even if I think about it and search

Below are the length calculation functions of the array with a value of 1 and the main function to run.

void arrlen(int arr[])

{

int len = sizeof(arr) / sizeof(int);
printf("%d", len);

}

int main(void)

{

int arr[10];
arrlen(arr);
return 0;

}