我正在尝试使用while循环从字符串中删除字母，直到没有剩下的为止。我在这里做错了什么？

#include<iostream>
#include<string>
using namespace std;

int main() {
    string word;
    cout << "please enter a word: ";
    getline(cin, word);
    int str_size;
    word.size() = str_size;
// the line above says "word must be modifiable". new to coding so not sure how to fix it?
// also haven't tested anything below this point yet.
    while (str_size) {
        word.resize(str_size - 1, '\0');
    }

    string end;
    getline(cin, end);
    return 0;
    }

谁能解释我在这里做错了什么。我只是以错误的方式去做吗？