求助关于结构体重载运算符

#include<bits/stdc++.h>
#define ll long long
using namespace std;
int a;
struct node
{
    int num,val;
    friend bool operator< (const struct node &a,const struct node &b)
    {
        return a.val<b.val;
    }
};
array<node,10001> s;
bool cmp(node a,node b)
{
    return a.val<b.val;
}
int main()
{
    int n;
    cin>>n;
    for(int i=1;i<=n;i++) cin>>s[i].num>>s[i].val;
    sort(s.begin()+1,s.end()+1,cmp);
    for(int i=1;i<=n;i++) cout<<s[i].num<<" "<<s[i].val<<endl;
    return 0;
}