Циклический двунаправленный список переделать в однонаправленный

//---------------------------------------------------------------------------
#include <stdio.h>
#include <vcl.h>
#pragma hdrstop
 
typedef struct Tinstrument  {
 
unsigned int ID;
char SName[10];
char Amount;
 
Tinstrument *next;
 
}   Tinstrument;
//---------------------------------------------------------------------------
#pragma argsused
int main(int argc, char* argv[])
{
    Tinstrument *list,
   *cur,
   *del,
   *last;
   list=last=NULL;
int d;
while(1) {
    printf("Nomer deystviya (0-Vyhod; 1-Vvod; 2-Vyvod; 3-Poisk;\n"
    "4-Udalenie): ");
    scanf("%d", &d);
    printf("\n");
    switch(d) {
        case 0:
        cur=list;
        if (list!=NULL)
         do {
        del=cur;
        delete del;
        cur=cur->next;
         } while (cur!=list);
        return 0;
 
        case 1:
        cur=last;
        if (list==NULL)
        {
        list=new Tinstrument;
        list->next=last;
        last=cur=list; }
        else {
        cur->next=new Tinstrument;
        cur->next=list;
        last=cur; }
        printf("Vvedite ID SName Amount  "
        "(cherez probel):\n");
        scanf("%u %s %c", &cur->ID, cur->SName, &cur->Amount);
        printf("\n");
        break;
 
        case 2:
        cur=list;
        printf("%6s %9s %5s\n", "ID", "SName", "Amount" );
 
         do {
        printf("%6u %9s %5c\n", cur->ID, cur->SName, cur->Amount );
        cur=cur->next;
         } while (cur!=list);
        printf("\n");
        break;
 
        case 3:
        char key;
        printf("Stroka dlya poiska po polu ID: ");
        scanf("%s", &key);
        cur=list;
        printf("%6s %9s %5s\n", "ID", "SName", "Amount" );
        if (list!=NULL)
         do {
             if (cur->ID,key)
              printf("%6u %9s %5c\n", cur->ID, cur->SName, cur->Amount );
              cur=cur->next;
         } while (cur!=list);
        printf("\n");
        break;
 
        case 4:
        int n;
        printf("Vvedite nomer udalyaemoy stroki: ");
        scanf("%d", &n);
        if (list->next==list) {
        delete list;
        list=last=NULL; }
        else
        if (n==1) {
        del=list;
        list=list->next;
        delete del; }
        else {
        cur=list;
        for (int i=3; i<=n; i++)
         cur=cur->next;
        del=cur->next;
        cur->next=del->next;
        delete del;
        if (cur->next==NULL)
        last=cur; }
        printf("Stroka %d uspeshno udalena. \n", n);
        printf("\n");
        break;
        default:
         printf("Nevernyi nomer deistviya.\n");
         printf("\n");
        }
    }
}
//---------------------------------------------------------------------------

#include <stdio.h>
 
#pragma hdrstop
 
typedef struct Tinstrument {
 
unsigned int ID;
char SName[10];
char Amount;
 
Tinstrument *next;
 
} Tinstrument;
//---------------------------------------------------------------------------
#pragma argsused
int main(int argc, char* argv[])
{
Tinstrument *list,
*cur,
*del,
*last;
list=last=NULL;
int d;
while(1) {
printf("Nomer deystviya (0-Vyhod; 1-Vvod; 2-Vyvod; 3-Poisk;\n"
"4-Udalenie): ");
scanf("%d", &d);
printf("\n");
switch(d) {
case 0:
cur=list;
if (list!=NULL)
do {
del=list;
list=del->next;
delete del;
cur=list;
} while (cur!=NULL);
return 0;
 
case 1:
 
 
cur=new Tinstrument;
cur->next=list;
list=cur;
printf("Vvedite ID SName Amount "
"(cherez probel):\n");
scanf("%u %s %c", &cur->ID, cur->SName, &cur->Amount);
printf("\n");
break;
 
case 2:
cur=list;
printf("%6s %9s %5s\n", "ID", "SName", "Amount" );
 
do {
printf("%6u %9s %5c\n", cur->ID, cur->SName, cur->Amount );
cur=cur->next;
} while (cur!=NULL);
printf("\n");
break;
 
case 3:
unsigned int key;
printf("Stroka dlya poiska po polu ID: ");
scanf("%6u", &key);
cur=list;
printf("%6s %9s %5s\n", "ID", "SName", "Amount" );
if (list!=NULL)
do {
if (cur->ID==key)
printf("%6u %9s %5c\n", cur->ID, cur->SName, cur->Amount );
cur=cur->next;
} while (cur!=NULL);
printf("\n");
break;
 
case 4:
int n;
printf("Vvedite nomer udalyaemoy stroki: ");
scanf("%d", &n);
/*if (list->next==list) {
delete list;
list=last=NULL; }
else*/
if (n==1) {
del=list;
list=list->next;
delete del; }
else {
cur=list;
for (int i=2; i<n; i++, cur=cur->next) ;
printf("%6u %9s %5c\n", cur->ID, cur->SName, cur->Amount );
del=cur->next;
cur->next=del->next;
delete del;
/*if (cur->next==NULL)
last=cur; }*/
 
printf("Stroka %d uspeshno udalena. \n", n);
printf("\n");
break;
default:
printf("Nevernyi nomer deistviya.\n");
printf("\n");
}
}
}
}
 
//---------------------------------------------------------------------------