Question

I have a problem with my homework assignment and I do not know where I went wrong with it. I have to design a function for radix sort with a a buckets and k rounds. I need to preserve the sequence of the list items in the bucket and therefore I need to keep two points for each bucket – to front and rear.
However, when I compile my code and run my test code with 10 numbers that need to be sorted, my output contains only 3 numbers. If its 20 numbers, it prints only 2. Can you help me please? This is my code and thank you for your time. Edit: by leastSigDig i mean Significant Digit i have to change that because its a bad name

#include <cstdlib> // Provides size_t and NULL
#include <iostream>
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
using namespace std;

struct listnode { struct listnode * next;
                  unsigned long     value; } ;

struct listnode *radixsort (struct listnode *data, int a, int k){
    struct listnode *front [a], *rear [a], *cursor;
    int i=0 , j = 0, leastSigDig,base10num;
    if (data == NULL) {return data;}

    for (i;i<k;i++){
        base10num= pow(a,i);
        cursor = data;
        for (j=0; j<a; j++){
            front [j] = NULL;
            rear [j] = NULL;
        }
        while (cursor != NULL){
            leastSigDig = ((cursor->value)/base10num)%a;
            if (rear [leastSigDig]!= NULL){
                rear[leastSigDig]->next= cursor;
                rear [leastSigDig]= cursor;
            }
            else if (cursor == NULL) {
                rear [leastSigDig] = cursor;
            }
            cursor = cursor->next;
        }

        //Linking
            cursor = NULL;
for (int y=0; y< a-1; y++){
    int z= y+1;
    if (front [y] == NULL)
        continue;
    else if (cursor == NULL){
            cursor = front [y];
            rear [y]->next = front [z];
        }
    else if (cursor != NULL) 
            rear [y]->next = front [z];


    data = cursor;
    }
        }
    }
    return data;
}   


int main(void)
{  
    long i, length=10;
    long a = 10; // working with base 10
    long k = log10(length*a);
    struct listnode *node, *space;
    space =  (struct listnode *) malloc(length*sizeof(struct listnode));
    for( i=0; i< length; i++ ) {
        (space + i)->value = 2*((17*i)%length);
        (space + i)->next = space + (i+1);
    }
    (space+(length-1))->next = NULL;
    node = space;
    struct listnode * temp =node;
    cout<<endl<<"List before radixsort\n" <<endl ;
    while(temp!=NULL)
    {
        cout << temp->value << "\t";
        temp = temp->next;
    }

    node = radixsort(node,a,k);

    listnode *check = node;
    cout << "\n\nList after radixsort \n\n";
    while (check)
    {
        cout << check->value << "\t";
        check = check->next;
    }
    cout << "\n\n";
    exit(0);
}

Answer 1

There is at least one problem here:

//Linking
int y= 0;

for (int y; y< a-1; y++){

The variable y in the for loop shadows the y in the outer scope. This means the y inside the loop is uninitialized and you are off into the weeds.

You should turn up the compiler warning level and pay attention to what it says.