我希望帮助在倒计时之间获得延迟，每行等于0.75秒，我尝试添加睡眠功能，并说它无法定义标识符
#include<iostream>
#include<dos.h>
using namespace std;
int main()
{
float a;
cout << "Lets do a countdown, write a number:" << endl;
cin >> (a);
while (a > 0) {
cout << a << endl;
a = a--;
}
cout << "Countdown Aborted" << endl;
system("pause");
}