求问最大值和最小值的差哪里有问题

#include<iomanip>
#include<iostream>
#include<cmath>
#include<cstring>
#include<string>
#include<algorithm>
#include<cstdio>
using namespace std;
int main(){
	int a[256];
	int maxn,minn;
	int len;
	cin>>len;
	for(int i=0;i<len;i++){
		cin>>a[i];
	}
	for(int i=0;i<len;i++){
		maxn=max(a[i],a[i+1]);
		minn=min(a[i],a[i+1]);
	}
	cout<<maxn-minn;
	return 0;
}

QAQ