思路与楼下大佬大致相同

#include <bits/stdc++.h>
using namespace std;
int main()
{
    int n, a[305], l, r, ans = 0;
    cin >> n;
    for (int i = 1; i <= n; i++)
        cin >> a[i];
    cin >> l >> r;
    for (int i = l; i <= r; i++)
        ans += a[i];
    cout << ans << endl;
    return 0;
}

#include <iostream>
using namespace std;
int main()
{
    int n,a[304],c,b,sum=0;
    cin >>n;
    for(int i=1;i<=n;i++)
    {
        cin >> a[i];
    }
    cin >> c >> b;
    for(int i=c;i<=b;i++)
    {
        sum+=a[i];
    }
    cout << sum;
}