关于while(i--)和while(--i)的理解

#include <iostream>
using namespace std;
int main()
{
	int i = 3;
	while(i--)//先取值后减 
	{
		cout << i << " ";//输出2 1 0 
	}
	cout << endl;
	i = 3;
	while(--i)//先减后取值 
	{
		cout << i << " ";//输出2 1 
	}
	cout << endl;
	return 0;
}