我一开始提交了一段这样的代码，在本地运行正常，没想到报错 WA : read ASCII 0 ,expect xxx：

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

// big num add

string a, b, ans;
int sizea, sizeb;

void add(){
	int carry = 0;
	int i = 0, j = 0, k = 0;
	while (i < sizea || j < sizeb || carry) {
		int digit1 = i < sizea ? a[i] - 48 : 0;
		int digit2 = j < sizeb ? b[j] - 48 : 0;
		int sum = digit1 + digit2 + carry;
		ans[k++] = (sum % 10) + '0';
		carry = sum / 10;
		i ++;
		j ++;
	}
}

int main(){
	cin >> a >> b;
	sizea = a.length();
	sizeb = b.length();
	ans.resize(max(sizea, sizeb) + 1);
	reverse(a.begin(), a.end());
	reverse(b.begin(), b.end());
	add();
	reverse(ans.begin(), ans.end());
	cout << ans << endl;
	return 0;
}

添加下面一个函数去除倒转字符串前的 ASCII 0 程序才得以运行：

string remove(string str) {
    while (!str.empty() && str[0] == '\0') {
        str.erase(str.begin());
    }
    return str;
}
// ...
cout << remove(ans) << endl;