What scanf("%d", array + i); does

Question

void get_elemnts(int *array, int max_index){
    for(int i = 0; i < max_index; i++){
        printf("enter element 0%d: ", i);
        scanf("%d", array + i);
    }
}

**scanf("%d", array + i);**Can someone explain? I have a code that gets the elements of an array from the user input. And at the moment I have difficulties with understanding what exactly this part of the code does

It iterates along `array` obtaining an input for each element. `array + i` is the same as `&array[i]`. — Weather Vane, Apr 04 '20 at 20:12
For any pointer or array `array` and index `i`, the expression `array[i]` is exactly equal to `*(array + i)`. From that follows that `&array[i]` will be equal to `array + i`. — Some programmer dude, Apr 04 '20 at 20:13
There must be a decent duplicate for this - but I can't find it with a quick search. — Adrian Mole, Apr 04 '20 at 20:14
I think reading this question will help you a lot (https://stackoverflow.com/a/381549/12330258) — hanie, Apr 04 '20 at 20:15

score 3 · Answer 1 · answered Apr 04 '20 at 20:25

There are three concepts involved:

scanf("%d", pointer) method will read the integer value (%d) from stdin and write it to the memory referenced by pointer.
Nature of arrays: arrays in C are stored linearly in memory: int array of size n is just n * sizeof(int) bytes in memory and the variable of the array is the same as the pointer to its first element.
Pointer arithmetic: array + i moves the pointer by i memory cells of type int which is i * sizeof(int) bytes. This is exactly where the i'th element of array is. So array + i is a pointer to array[i].

Vlad from Moscow · Accepted Answer · 2020-04-04T20:28:21.890

This function definition

void get_elemnts(int *array, int max_index){
    for(int i = 0; i < max_index; i++){
        printf("enter element 0%d: ", i);
        scanf("%d", array + i);
    }
}

is equivalent to

void get_elemnts(int *array, int max_index){
    for(int i = 0; i < max_index; i++){
        printf("enter element 0%d: ", i);
        scanf("%d", &array[i] );
    }
}

This expression array + i gives pointer to the i-th element of the array.

The format %d used in the function scanf expects a pointer to an object of the type int and this expression array + i yields the pointer using the pointer arithmetic.

The expression array[i] is equivalent to the expression *( array + i ).

So the expression &array[i] is the same as &*( array + i ) where the applied operators &* can be omitted and you will get just ( array + i ).

What scanf("%d", array + i); does

2 Answers2