如何解决 freopen 和 scanf ( C++ ) 的问题？

Question

我为 USACO 银牌问题“休息站”（2018 年 2 月）编写了一些代码。 但是，当我提交代码时，freopen 和 scanf 存在一些问题。

我尝试更改 to 并添加 return 0，但它们都不起作用。 我包含了 stdio.h、算法和向量库。

using namespace std;

typedef pair < int, int > ii;

int l, n, rf, rb;
vector < pair < int, int > > map;

int main() {

    freopen("reststops.in", "r", stdin);
    freopen("reststops.out" "w", stdout);

    scanf("%d %d %d %d", &l, &n, &rf, &rb);
    for(int i = 0; i < n; i ++) {
        int x, c;
        scanf("%d %d", &x, &c);
        map.push_back(ii(x, c));
    }
    int start_idx = 0; int start = 0;
    int maxi = 0; int max_idx = 0;
    int ans = 0;

    while(true) {
        bool flag = false;
        for(int i = start_idx; i < map.size(); i ++) {
            if(maxi < map[i].second) {
                max_idx = i;
                maxi = map[i].second;
                flag = true;
            }
        }
        if(!flag) {
            if(start_idx == map.size() - 1) break;
            else {
                ans += (rf - rb) * (map[map.size() - 1].first - map[start_idx].first);
                break;
            }
        }
        if(start_idx == 0) start = 0;
        else start = map[start_idx].first;
        int curr_f = (map[max_idx].first - start) * rf;
        int curr_b = (map[max_idx].first - start) * rb;
        ans += (curr_f - curr_b) * map[max_idx].second;
        start_idx = max_idx;
    }
    printf("%d", ans);
    return 0;

}

编译错误

main.cpp: In function ‘int main()’:
main.cpp:14:40: error: cannot convert ‘_IO_FILE*’ to ‘const char*’ for argument ‘2’ to ‘FILE* freopen(const char*, const char*, FILE*)’
     freopen("reststops.out" "w", stdout);
                                        ^
main.cpp:13:40: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result]
     freopen("reststops.in", "r", stdin);
                                        ^
main.cpp:16:43: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d %d %d %d", &l, &n, &rf, &rb);
                                           ^
main.cpp:19:31: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result]
         scanf("%d %d", &x, &c);
                               ^