c - Do we have to create an even and an odd array?

Question

How can we modify the following code (which initially asks the user for 10 numbers to be entered, get stored in an array, and printed on the screen) so that the even numbers are printed on the first line, and the odd on the second:

#include <stdlib.h>
#include <stdio.h>
int i,j;
int array_1[10];
int main() {
    for(i=0;i<10;i++) {
    printf("Enter a number: ");
        scanf("%d", &array_1[i]);
    }
    printf("The elements of the array are: ");
    for (j=0;j<10;j++) {
        printf("%d ", array_1[j]);
    }
    printf("
");
    return 0;
}

question from:https://stackoverflow.com/questions/65911603/do-we-have-to-create-an-even-and-an-odd-array

Answer 1

O(n) Solution:

you have to add odd numbers at the back of the array and add the even numbers at the front of the array and keep track of the indexes.

int array_1[10];

int main() {

    int even = 0, odd = 10;

    for (int i = 0; i < 10; i++) {
        printf("Enter a number: ");
        int inp;
        scanf("%d", &inp);
        if (inp % 2 == 0) {
            array_1[even++] = inp;
        } else {
            array_1[--odd] = inp;
        }
    }

    // even numbers
    for (int i = 0; i < even; i++) {
        printf("%i ", array_1[i]);
    }
    printf("
");

    // odd numbers
    for (int i = 9; i >= odd; i--) {
        printf("%i ", array_1[i]);
    }
    printf("
");

    return 0;
}