PTA----- 數字加密 (15分)

#include<stdio.h>
int main()
{
    int i = 3, x;
    int a[4];
    int temp;
    scanf("%d", &x);
    while (i != -1) 
    {
        a[i] = x % 10;
        x = x / 10;
        i--;
    }
    for (i = 0; i < 4; i++)
    {
        a[i] = a[i] + 9;
    }
    for (i = 0; i < 4; i++)
    {
        a[i] = a[i] % 10;
    }
    for (i = 0; i < 2; i++)
    {
        temp = a[i];
        a[i] = a[i + 2];
        a[i + 2] = temp;
    }
    printf("The encrypted number is ");
    for (i = 0; i < 4; i++)
    {
        printf("%d", a[i]);
    }
    return 0;
}