Question

If I write the code like this below?

int arr[] = {6, 7, 8, 9, 10};
int *ptr = arr;
*(ptr++)+= 123;

what’s the elements in the arr[] now?

I originally thougt the arr[] now should be {6, 130, 8, 9, 10}, but actully the result is {129, 7, 8, 9, 10}, I don’t know why?

In my opinion, ptr++ is in the bracket, so the ptr should increase first, isn’t it? after it increased one, it should point to the second element in the array.

Answer 1

The value of ptr++ is the value of ptr before any increment (the side-effect is incrementing ptr at some time during the evaluation of the expression).

That is the value that is dereferenced in *(ptr++).

If you dereference ptr in a subsequent expression, it points to the next element, the one with value 7.