Radix sort c++ implementation - c++

Question

I am having trouble trying to implement a radix sort. This is an assignment, and my professor is less than willing to even point me in the right direction. I have been staring at this code for a long time. Can someone explain to me why my pointers are not working? I did some inspection, and saw that my pointer is not even pointing to the next pointer, and I am very confused as to why. I am not asking for anyone to do my assignment, just some direction.
#include <iostream>
#include <stdio.h>
#include <time.h>
#include <stdlib.h>
#define COLUMN 10
using namespace std;
struct List{
int data;
List *p;
};
struct node{
int len = 0;
List *p = NULL;
};
void printList(int list[], int len){
for (int i = 0;i<len;i++){
cout <<list[i] << " ";
}
cout << "\n";
}
void deleteList(node columns[], int len){
for (int j =0; j<COLUMN;j++){
List *curr;
List *prev;
curr = columns[j].p;
for (int i = 0; i<len;i++){
prev = curr;
curr = curr->p;
delete prev;
}
delete curr;
}
}
void overrideArray(node columns[], int a[], int len){
int k = 0; List *curr;
for (int i = 0;i<COLUMN,k<len;i++){
int len = columns[i].len;
cout << len << " length"<< endl;
curr =columns[i].p;
for (int j = 0;j<len;j++){
cout << "plue\n";
if (len == 0) continue;
cout << k <<" plue2\n";
a[k]=curr->data;
cout << "plue3\n";
cout << a[k] << " value";
curr = curr->p;
k++;
}
}
printList(a,len);
}
int main(){
srand(time(NULL));
int length = 10, m,n,i;
node *columns = new node[COLUMN];
List * curr;
int *a = new int [length];
for (int i = 0;i<length;i++){
a[i] = 2;
}
printList(a,length);
m = 10; n = 1; i =0;
while(columns[0].len!=length){
int loc = (a[i]%m)/n;
//cout << loc << endl;
curr = columns[loc].p;
while(curr != NULL){
//cout << "here" << endl;
curr = curr->p;
//cout << curr->data << endl;
}
curr = new List;
cout << curr->p << endl;
curr->data = a[i];
cout << curr->p << endl;
columns[loc].len++;
i++;
if (i == length-1){
overrideArray(columns,a,length);
cout << "here5\n";
deleteList(columns,length);
cout << "here6\n";
i = 0;
m *= 10;
n*=10;
}
}
overrideArray(columns,a,length);
printList(a,length);
return 0;
}