Please help!
The following code is supposed to sort the nodes by switching the pointers
instead of data, but all I get is an infinite loop when I run it.


#include <stdio.h>
#include <cstdlib>
#define HOWMANY 20

using namespace std;

class Stack;

class Node
{
public:
Node (double);
friend class Stack;
private:
double data;
Node* next;
};

#define NodeNULL (Node *)(0)

Node::Node(double thisdata):data(thisdata),next(NodeNULL)
{

}

class Stack
{
public:
Stack();
void push(double);
double pop();
void selectionsort();
private:
Node* top;
};

Stack::Stack():top(NodeNULL) { }

void Stack:ush(double newguy)
{
Node* tptr = new Node(newguy);
tptr->next = top;
top = tptr;
}

double Stack:op()
{
Node* tptr;
double tdata;
if(top==NodeNULL){
fprintf(stderr,"empty stack\n");
exit(1);
}
tdata = top->data;
tptr = top;
top = top->next;
delete tptr;
return(tdata);
}

void Stack::selectionsort()
{

int icount = 0;
int count = 0;
double bestvalue;
Node *i = top;
Node *iprev = i;
Node *j = top;
Node *jprev = i;
Node *iprevtemp;
Node *jprevtemp;
Node *tempi;
Node *tempj;
Node *temp2;
Node *tempjprev;

while (i->next != NodeNULL) {

bestvalue = i->data;
tempj = i;
jprev = i;
j = i->next;

while (j->next != NodeNULL) {

if (j->data < bestvalue) {
bestvalue = j->data;
tempjprev = jprev;
tempj = j;
}

jprev = j;
j = j->next;

}

//Switching

tempi = i;
iprevtemp = iprev;
jprevtemp = tempjprev;

jprevtemp->next = tempi;
iprevtemp->next = tempj;

temp2 = tempj->next;
tempj->next = tempi->next;
tempi->next = temp2;

i = tempj;

iprev = i;
i = i->next;
}

}

double genrand()
{
return(((double)(random())+1.0)/((double)(RAND_MAX)+2.0));
}

int main(int argc, char** argv)
{
int i;
Stack q;

srandom(123456789);
for(i=0;i<HOWMANY;i++) q.push(genrand());
q.selectionsort();
for(i=0;i<HOWMANY;i++) printf("%f\n",q.pop());
}