为啥显示变量i undeclared?

#include <iostream>
using namespace std;
int n,p[1000010],d,sp[100000010],ans;
int main()
{
    cin>>n>>d;
    for (int i=1;i<=n;i++)
        cin>>p[i],sp[p[i]]=1;
    int j=1;
    for (int i=0;j<=n;j++)
        i=p[j];
        for (int k=i+1;k<=i+d;k++)
            if (sp[k]==1)
                ans++;
    cout<<ans;   
    return 0;
}