1.c

#include<stdio.h>
#include<windows.h>

DWORD summ(DWORD a)
{
  __asm
  {
    push ebx
    push edx
    push esi

    xor esi, esi
    mov eax, a
    mov bx, 10
  a_div:
    xor edx, edx
    div bx
    add esi, edx
    cmp ax, 0
    jne a_div
    mov eax, esi

    pop esi
    pop edx
    pop ebx
  }
}

int main()
{
  DWORD i, j;

  printf("Specify number which you want to change: ");
  scanf_s("%d", &i);

  j = summ(i);

  printf("%d.\n", i);

  system("pause");
  return 0;
}

2.c

#include<stdio.h>
#include<windows.h>

DWORD summ(DWORD a)
{
  DWORD result;
  __asm
  {
    push eax
    push ebx
    push edx
    push esi

    xor esi, esi
    mov eax, a
    mov bx, 10
  a_div:
    xor edx, edx
    div bx
    add esi, edx
    cmp ax, 0
    jne a_div
    mov result, esi

    pop esi
    pop edx
    pop ebx
    pop eax
  }
  return result;
}

int main()
{
  DWORD i, j;

  printf("Specify number which you want to change: ");
  scanf_s("%d", &i);

  j = summ(i);

  printf("%d.\n", i);

  system("pause");
  return 0;
}