unsigned long int a=213121122012;
要变成int c[];
 c[0]=2; c[1]=1; c[2]=3; c[3]=1.......c[11]=2;

代码怎么写？

#include <stdio.h>
#include <string.h>

int main() {

  unsigned long int a = 213121122012;
  char str[50];

  sprintf(str, "%lu", a);

  int i = 0;
  while(str[i] != '\0') {
    printf("%d: %c\n", i, str[i]);
    i++; 
  }

  return 0;
}

int main()
{
    unsigned long long a = 213121122012;
    unsigned long long b = a;
    int c[20], len = 0, t;

    while (b)
    {
        c[len++] = b % 10;
        b /= 10;
    }

    for (int i = 0; i < len / 2; i++)
    {
        t = c[i];
        c[i] = c[len - i - 1];
        c[len - i - 1] = t;
    }

    for (int i = 0; i < len; i++)
    {
        printf("c[%d]=%d; ", i, c[i]);
    }

    return 0;
}