while((cin>>x)&&(x!=0))就可以了

while(x)
{ cin>>x;
...

死循环！

连空间声明都写错地方了

#include <iostream>
using namespace std;
 
int main()
 {
   
    double x;
     double sum = 0;
 
    while (cin>>x,x) //添加逗号运算符。因为cin返回值始终为1，直到遇见文件结束符ctrl+z
{
         sum = sum + x;
         cout << "Now, sum = " << sum << endl;
     }
 
    cout << "Input 0, Warnnig.......\nTerminated!";
     cin.get();
     cin.get();
     return 0;
 }