C++ insert and delete characters in a linked list - c++

Question

My problem is that I'm trying to insert a letter into a linked list based on users input at a specific position given by the int h...However every time I run the program only the second character in the list changes regardless of the number the user puts into the program.
Example:
./h
Name: koala
a<-l<-a<-o<-k
Change the position: 2
To the character: 3
a<-l<-3<-o<-k
Insert the Character: F
To the Postion: 3
a<-F<-l<-3<-o<-k
I want it to look like.
./h
Name: koala
a<-l<-a<-o<-k
Change the position: 2
To the character: 3
a<-l<-3<-o<-k
Insert the Character: F
To the Postion: 3
a<-l<-3<-F<-o<-k
I know my problem is in the insert_char() function in my lists.cpp but just can't figure out what i'm doing wrong...
List.h
#include <iostream>
using namespace std;
struct Node;
Node* new_list();
void insert_front(Node** plist,char x);
void insert_char(Node* plist, char x, int p);
void change_char(Node* plist, char x, int p);
void print_list(Node* list);
void delete_front(Node** plist);
void delete_list(Node** plist);
//void delete_char(Node* plist,int p);
struct Node {
char x;
Node *next;
};
main.cpp
struct Node {
char x;
Node *next;
};
int main(){
Node *list;
list = new_list(); //new empty list
cout<<"Name: ";
string name;
cin>> name;
for (int i =0; i < name.length(); i++)
insert_front(&list, name[i]);
//---------print list-------------------------
print_list(list);
cout <<"Change the position: ";
int z;
cin>> z;
cout<< "To the character: " ;
char x;
cin>> x;
change_char(list, x, z);
print_list(list);
cout <<"Insert the Character: ";
char y;
cin>> y;
cout<< "To the Postion: ";
int h;
cin>> h;
insert_char(list, y, h);
print_list(list);
return 0;
}
lists.cpp
Node* new_list()
{
Node* list = 0; //in C++ it is better to use 0 than NULL
return list;
}
void insert_front(Node** plist,char x){
Node* t;
t = new Node;
t->x = x;
t->next = *plist;
*plist = t;
return;
}
void change_char(Node* plist, char x, int p)
{
Node* s = plist;
for (int i=1; i<p && 0!=s;i++)
s = s->next;
if (0 != s)
s->x = x;
return;
}
void insert_char(Node* plist, char x, int p){
Node* s = plist;
Node* a = new Node();
for (int i=1; i<p && s; i++)
a->next=s->next;
s->next=a;
if (0 !=s)
a->x=x;
return;
}
//void delete_char(Node* plist,int p)
void print_list(Node* list){
Node* p;
p = list;
if(p == 0)
cout << "--- empty list ---" << endl;
while(p !=0){
cout << p->x<<"<-";
p = p->next;
}
cout << endl;
}
void delete_front(Node** plist){
Node* t;
if( *plist != 0){ // list is not empty
t = (*plist);
*plist = (*plist)->next;
delete t;
}
}
void delete_list(Node** plist){
while(*plist != 0) //while list not empty
delete_front(plist);
}
bool is_empty(Node* list){
return (list == 0);
}

Answer 1

The for loop in insert_char is just "inserting" the character over and over. I think you meant to advance s to the starting point of the insertion (as determined by h).
Update:
This part is wrong for a few reasons:
for (int i=1; i<p && s; i++)
a->next=s->next;
s->next=a;
Note that the indentation is misleading. Since you don't have braces, only the middle line is part of the loop. Effectively, you've written:
for (int i=1; i<p && s; i++) {
a->next=s->next;
}
s->next=a;
Personally, I always use braces on blocks, even if they consist of only one statement.
So you set a->next a bunch of times instead of advancing to the point in the list you want to go.
You need to advance to the position you want the new element in the loop, and then do the actual insertion.
// Advance s to index p.
for (int i = 1; i < p && s->next; i++) {
s = s->next;
}
// Insert a at s.
a->next = s->next;
s->next = a;