what is the use of equal sign two times in statement : In c language, what is the use of equal sign twice in statement. for example in following code statement -  *arr += *(arr + n - 1) += 10;  has twice equal sign

    #include <stdio.h>
    #define SIZE(arr) sizeof(arr) / sizeof(*arr);
    void fun(int* arr, int n)
    {
    int i;
    *arr += *(arr + n - 1) += 10;
    }
    void printArr(int* arr, int n)
    {
    int i;
    for(i = 0; i < n; ++i)
    printf("%d ", arr[i]);
    }
    int main()
    {
    int arr[] = {10, 20, 30};
    int size = SIZE(arr);
    fun(arr, size);
    printArr(arr, size);
    return 0;
    }