方法一：

int main()
{
  int  ival, n = 0;
  char bin[32];
  scanf("%d", &ival);
  while(ival > 0) {
    bin[n++] = ival % 2;
    ival /= 2;
  }
  for(n–; n >= 0; n–)
    printf("%d", bin[n]);
  printf("n");
  getch();
}

方法二：

int main()
{
  int  ival, n = 0;
  char bin[32];
  scanf("%d", &ival);
  while(ival > 0) {
    bin[n++] = ival & 0x01;
    ival >>= 1;
  }
  for(n–; n >= 0; n–)
    printf("%d", bin[n]);
  printf("n");
  getch();
}