Linked list exercise in C, what is wrong? - linked-list

Question

The code below does compile, but it doesn't run as it should.
I'm not sure what am I doing wrong, so would someone be willing to tell me what I did wrong and what I should have done better.
What do I need to change to make it run properly?
#include<stdio.h>
#include<stdlib.h>
typedef struct sub_Node
{
int value;
struct sub_Node *next;
}sub_Node;
typedef struct Node
{
char *name;
struct Node *next;
struct sub_Node *sub_start;
}Node;
Node *start;
void add_player(char *name)
{
Node *temp;
temp = (Node *)malloc(sizeof(Node));
temp->next = start;
temp->name = name;
temp->sub_start = (sub_Node *)malloc(sizeof(sub_Node));
temp->sub_start->next = NULL;
temp->sub_start->value = -1;
start = temp;
}
void initialize()
{
char *p;
p = "\0";
add_player(p);
}
void remove_player(char *name)
{
Node *p;
for(p = start; p!= NULL; p = p->next)
if(p->name == name)
{
p->name = p->next->name;
p->next = p->next->next;
}
}
sub_Node* add_descending(sub_Node* sub_start, int piece_value)
{
sub_Node *temp, *prev, *next;
temp = (sub_Node *)malloc(sizeof(sub_Node));
temp->value = piece_value;
temp->next = NULL;
prev = NULL;
next = sub_start;
while(next && next->value >= piece_value)
{
prev = next;
next = next->next;
}
if(!next)
{
prev->next = temp;
}
else
{
if(prev)
{
temp->next = prev->next;
prev->next = temp;
}
else
{
temp->next = sub_start;
sub_start = temp;
}
}
return sub_start;
}
void add_piece(char *name, int piece_value)
{
Node *p;
int c;
for(p = start; p!=NULL; p = p->next)
if(p->name == name)
p->sub_start = add_descending(p->sub_start, piece_value);
}
void print_pieces(char *name)
{
Node *p;
sub_Node *q;
for(p = start; p!=NULL; p = p->next)
if(p->name == name)
{
printf("The values of the owned pieces are:");
for(q = p->sub_start; q->value != -1; q = q->next)
printf(" %d", q->value);
}
}
int lose_piece(char *name)
{
Node *p;
sub_Node *q;
int aux;
for(p = start; p!=NULL; p = p->next)
if(p->name == name)
{
for(q = p->sub_start; q->next->value != -1; q = q->next) {}
aux = q->value;
q->value = q->next->value;
q->next = q->next->next;
return aux;
}
}
void print_players()
{
Node *p;
printf("The players are: ");
for(p = start; p->name != "\0"; p = p->next)
printf("%s ", p->name);
printf("\n");
}
int main()
{
initialize();
int y, value;
char name[20];
printf("Insert a digit to execute the desired task:\n"
"<0> end the program\n"
"<1> add a player, who doesn't own any piece yet\n"
"<2> remove a player and all his pieces\n"
"<3> print the name of all the players\n"
"<4> a player gets a piece\n"
"<5> a player loses the piece with the lowest value out of the ones that he has\n"
"<6> prints the pieces of a player in a descending order by value\n\n");
do
{
printf("digit: ");
scanf("%d", &y);
switch(y)
{
case 1:
printf("Insert the player's name: ");
scanf("%s", name);
add_player(name);
break;
case 2:
printf("Insert the player's name: ");
scanf("%s", name);
remove_player(name);
break;
case 3:
print_players();
break;
case 4:
printf("Insert the player's name: ");
scanf("%s", name);
printf("Insert the value of the piece: ");
scanf("%d", value);
add_piece(name, value);
break;
case 5:
printf("Insert the player's name: ");
scanf("%s", name);
printf("\nThe player loses the piece: %d\n", lose_piece(name));
break;
case 6:
printf("Insert the player's name: ");
scanf("%s", name);
print_pieces(name);
}
} while(y != 0);
return 0;
}

Answer 1

your two main problems where this scanf("%d", value); value should be passed by reference like this scanf("%d", &value); and the second is string comparison in c as in your code p->name != "\0" and if(p->name == name) this is wrong because actually you are making comparison between addresses of strings (where it resides in memory) not strings values. to compare strings in c you have to use strcmp and families.
Actually 3 main problems. for setting string values as you did in temp->name = name; is little bit more complicated than that. because you are assigning to temp->name a string from the stack that is volatile (the stack will be more likely invalid soon you return from the function) . in your case you have to alloc a new string by using malloc (and friends) or just by using strdup.
here is as a bonus a slightly rewrite of your program, you will find many advises and is a good starting point for how to structure your code for an easy maintenance.
still want to advise you to change members and variables to more declarative names as in sub_start and sub_Node can be PieceNode and pieces respectively.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
typedef struct sub_Node
{
int value;
struct sub_Node *next;
}sub_Node;
typedef struct Node
{
char *name;
struct Node *next;
struct Node *prev; // this to make life easyer
struct sub_Node *sub_start;
}Node;
Node *start = NULL;
Node *find_player(char *name){
Node *tmp = start;
while( tmp ){
if(strcmp(tmp->name,name) == 0 )
break;
tmp = tmp->next;
}
return tmp;
}
// int to return Error Code
//
int add_player(char *name)
{
Node *temp;
if( find_player(name)) {
printf("player %s already exists\n", name);
return 1;
}
// do not cast malloc
temp = malloc(sizeof(Node));
if( !temp ){
printf ("not enough memory\n");
return 2;
}
temp->name = strdup ( name); // here was your error
temp->sub_start = NULL; // keep it simple
temp->prev = NULL;
temp->next = start;
if(start)
start->prev = temp;
start = temp;
return 0; // no error
}
void DestroyPieces(sub_Node* piece){
if( piece ) {
DestroyPieces( piece->next );
free( piece );
}
}
// as usual use int to return error code
int remove_player(char *name)
{
Node *player = find_player(name);
if ( !player ){
return 1; // player not found
}
if ( player->next ){
player->next->prev = player->prev;
}
if ( player->prev ){
player->prev->next = player->next;
}
DestroyPieces(player->sub_start);
free(player->name);
free(player);
return 0; // success
}
sub_Node* new_piece(int value){
sub_Node *temp = malloc( sizeof(sub_Node) );
if(temp){
temp->value = value;
temp->next = NULL;
}
return temp;
}
// int to return error code
// pass sub_start as pointer to pointer, as it might be updated
int add_descending(sub_Node** psub_start, int piece_value)
{
sub_Node *piece, *current, *prev = NULL;
if( !psub_start){
return 5; // this should not happen
}
current = *psub_start;
piece = new_piece( piece_value );
if( !piece ) return 1; // no mem
if(!current){
// this is the first and only one
*psub_start = piece;
return 0; // OK
}
while(current && current->value >= piece_value)
{
prev = current;
current = current->next;
}
if( prev )
prev->next = piece;
piece->next = current;
if( current == *psub_start ){
*psub_start = piece;
}
return 0 ; // OK
}
void add_piece(Node * player, int piece_value)
{
if ( !player) {
return ;
}
if(add_descending (&(player->sub_start), piece_value) == 0 )
return ; //OK
printf("an error occured while adding a piece (%d) to player '%s'\n",piece_value,player->name);
}
void print_pieces(Node *player)
{
sub_Node *q;
if( !player ){
return;
}
if( !player->sub_start ){
printf("Player '%s' has no pieces\n",player->name);
return;
}
printf("The values of the owned pieces are:");
for(q = player->sub_start; q != NULL; q = q->next)
printf(" %d", q->value);
printf("\n");
}
void lose_piece(Node *player)
{
if( !player ){
return;
}
sub_Node *q, *prev = NULL;
int aux;
if( !player->sub_start ){
printf("Player '%s' has no pieces\n",player->name);
return;
}
// i think you want drop the last one
for(q = player->sub_start; q->next != NULL ;prev = q, q = q->next) {
;
}
if(prev)
prev->next = NULL;
else
player->sub_start = NULL;
aux = q->value;
free(q);
printf("\nThe player loses the piece: %d\n", aux);
return;
}
void print_players()
{
Node *p;
if( !start ){
printf("there are no players, try to add some\n");
return;
}
printf("The players are: ");
for(p = start; p != NULL; p = p->next)
printf("%s ", p->name);
printf("\n");
}
void print_menu(void){
printf("Insert a digit to execute the desired task:\n"
"<0> end the program\n"
"<1> add a player, who doesn't own any piece yet\n"
"<2> remove a player and all his pieces\n"
"<3> print the name of all the players\n"
"<4> a player gets a piece\n"
"<5> a player loses the piece with the lowest value out of the ones that he has\n"
"<6> prints the pieces of a player in a descending order by value\n\n");
}
Node * get_player(char *name){
Node *player = find_player(name);
if(!player)
printf("Player '%s' do not exists\n",name);
return player;
}
int main()
{
// initialize(); no more needed
int y, value;
char name[20];
Node *player;
print_menu();
do
{
printf("digit: ");
scanf("%d", &y);
switch(y)
{
case 1:
printf("Insert the player's name: ");
scanf("%s", name);
add_player(name);
break;
case 2:
printf("Insert the player's name: ");
scanf("%s", name);
player = get_player(name);
if( player )
break;
case 3:
print_players();
break;
case 4:
printf("Insert the player's name: ");
scanf("%s", name);
player = get_player(name);
if( player ){
printf("Insert the value of the piece: ");
scanf("%d", &value);
add_piece(player, value);
}
break;
case 5:
printf("Insert the player's name: ");
scanf("%s", name);
player = get_player(name);
lose_piece(player);
break;
case 6:
printf("Insert the player's name: ");
scanf("%s", name);
player = get_player(name);
print_pieces(player);
}
} while(y != 0);
return 0;
}