为什么修改了变量的类型，程序就运行不了；我把num和add的类型改为char，就得不到想要的结果

Question

#include <iostream>int main(){ using namespace std; double num = 0; double add = 0; cout << "input the number: "; cin >> num; while (num!=0) { add += num; cout << "input the number again: "; cin >> num; } cout << "the total of these number is " << add << endl; return 0;}