How to use scanf() correctly when reading input into an array using pointers?

Question

For some reason, reading input using scanf() won't work this way:

int main() {
    int arr1_size = 0;

    // Reading array size
    scanf("%d", &arr1_size);

    int* arr1 = (int*) malloc(sizeof(int) * arr1_size);

    // Reading and printing array values
    for(int i = 0; i < arr1_size; i++) {
        scanf("%d", arr1);
        arr1++;
    }
    for(int i = 0; i < arr1_size; i++) {
        printf("%d", arr1[i]);
    }

    return 0;
}

What could be the issue?

Answer 1

Here is a slightly improved version of your program:

#include <stdio.h>
#include <stdlib.h>


int main() {
    int arr1_size = 0;

    printf("Hello,\nPlease enter the size of the first array:");
    scanf("%d", &arr1_size);

    int *arr1 = (int*) malloc(sizeof(int) * arr1_size);

    printf("\nPlease enter arr1 of size %d:\n", arr1_size);
    for(int i = 0; i < arr1_size; i++) {
        scanf("%d", arr1 + i);
    }
    printf("\nArray contents:\n");    
    for(int i = 0; i < arr1_size; i++) {
        printf("%d \n", arr1[i]);
    }

    return 0;
}

Execution:

./scan
Hello,
Please enter the size of the first array:3

Please enter arr1 of size 3:
1
2
3

Array contents:
1 
2 
3