不用while, if , ?: ,输出n到m，再从m到n，例如1,2,3,4,5,4,3,2,1
bool foo(int n, int m)
{
return printf("%d\n",n) && ( n==m || foo(n+1, m) ) && ( n==m || printf("%d\n",n) );
}
不用while, if , ?: ,输出n到m，再从m到n，例如1,2,3,4,5,4,3,2,1
bool foo(int n, int m)
{
return printf("%d\n",n) && ( n==m || foo(n+1, m) ) && ( n==m || printf("%d\n",n) );
}