我对这条线感到困惑:
sum += a[s[i] - '0'];
为了给出一些上下文,这是代码的其余部分:
#include <iostream>
using namespace std;
int main() {
int a[5];
for (int i = 1; i <= 4; i++)
cin >> a[i];
string s;
cin >> s;
int sum = 0;
for (int i = 0; i < s.size(); i++)
sum += a[s[i] - '0'];
cout << sum << endl;
return 0;
}