Problem with insertion function in linked list (pointers)

**kekewong** · 10-08-2009

Hi, i have a weird problem... Please see my code below:

Code:

void insert(struct record *start) 
{
	char name[30],name1[30],flag=' ';
	struct record *temp,*curr, *prev;
	curr=start;  
	printf("\n Enter name to insert :");
	gets(name);fflush(stdin);
	printf("\n Enter the name before which to insert:");
	gets(name1);fflush(stdin);
	
	while(curr->next != NULL && flag == ' ')  
	{       
                     if(strcmp(curr->name,name1)== 0) //PROBLEM WITH THIS SECTION,TRYING TO ADD BEFORE FIRST NODE
                     {
                                       flag='*';
                                       temp=(struct record *) malloc(sizeof(struct record));
                                       strcpy(temp->name,name);
                                       temp->next = curr;
                                       curr = temp;
                                       printf("\n Insertion done !");
                                       getch();
                                       break;
                     }
          
		else if(strcmp(curr->next->name,name1)== 0) // insert before second note , third, fourth ,etc
		{	
                                    flag='*';
			temp=(struct record *) malloc(sizeof(struct record));
                                    prev  = curr;
			strcpy(temp->name,name);
			temp->next = prev->next;
			prev->next =temp;
			printf("\n Insertion done !");
			break;
		}
		else
			curr=curr->next;
	}
	       if(flag==' ')
		printf("\n Record not found !");
		getch();
}

This code user can choose determine where to insert the name according what user type. i can insert the name before second node, but, i cant insert it BEFORE THE FIRST NODE. That means , if i insert the new node before my first node, then the new node will became my first note. My code looks fine but doesn't work, any solution?

**tabstop** · 10-08-2009

Your code doesn't look fine at all. It is impossible to write an insert-into-a-linked-list function with the prototype

Code:

void insert(struct record *)

You can have

Code:

struct record * insert(struct record *)

(where you return the new head of the list) or you can have

Code:

void insert(struct record **)

(where the address of the head of the list is passed in so that the head of the list can be modified).

**kekewong** · 10-08-2009

hmm ok ..

Code:

                                       temp->next = curr;
                                       curr = temp;

Does the code above is correct ? replacing the first node as temp.

**tabstop** · 10-08-2009

Think for ten seconds. If you have this function:

Code:

int this_doesnt_work(int x) {
    x = 10;
}

do you expect the value passed in to change in your original function? No.

So when you have

Code:

void insert(struct record *start)

it is not physically possible to change the value of start. It cannot be done.

**RockyMarrone** · 10-08-2009

Where is the first node or head node can u tell how u want to add the nodes ??

**kekewong** · 10-09-2009

hmm.. TabStop thanks for the solution, but it still doesn't works. Anywhere went wrong???

lol, sorry i still learning pointers . Lecturer just pass me the question and call us to fix the codes =.= so ... i let you guys see the full code that the lecturer want us to correct it (i have correct half way ):

Code:

#include<stdio.h>
#include<stdlib.h>
#include<string.h>

struct record
{
	char name[30];
	struct record *next;
};

void main()
{
	int choice;
	char ans;

    struct record *insert(struct record *), *append(struct record *);  //prototype
     void view(struct record *);//prototype
	struct record *del(struct record *); //prototype
	struct record *start;

	
	start=(struct record *)malloc(sizeof(struct record));
	start->next=NULL;
    
	do
	{
		system("cls");
		printf("\n\n 1. Insert");
		printf("\n 2. Deletion");
		printf("\n 3. View");	
		printf("\n 4. Append");
		printf("\n 5. EXIT");
		printf("\n\n Choice:");
		scanf("%d",&choice);fflush(stdin);

		switch(choice)
		{
		case 1:
			insert(start);
			break;
		case 2:
			del(start);
			break;
		case 3:
			view(start);
			break;
		case 4:
			append(start);
			break;
		case 5:
			 exit(0);
		default:
			printf("\n Invalid Choice ");
		}
	}while(choice!=99);
}


 struct record *insert( struct record *start) 
{
	char name[30],name1[30],flag=' ';
	struct record *temp,*curr, *prev ,*list;
	curr=start;  
	printf("\n Enter name to insert :");
	gets(name);fflush(stdin);
	printf("\n Enter the name before which to insert:");
	gets(name1);fflush(stdin);
	
	while(curr != NULL && flag == ' ')  
	{       
                        if(strcmp(curr->name,name1)== 0)
                              {
                                 flag='*';
                                 temp=(struct record *) malloc(sizeof(struct record));
                       	         strcpy(temp->name,name);
                                 temp->next = curr;
                                 curr = temp;
                                 printf("\n Insertion done !");
                                 getch();
         	                     return start;
                      	        break;
                               }
          
		else if(strcmp(curr->next->name,name1)== 0)
		            {	flag='*';
            			temp=(struct record *) malloc(sizeof(struct record));
                                                prev  = curr;
            			strcpy(temp->name,name);
            			temp->next = prev->next;
            			prev->next =temp;
            			 getch();
            			printf("\n Insertion done !");
            			return start;
            			break;
		              }
		else
			curr=curr->next;
	}
	if(flag==' ')
		printf("\n Record not found !");
		getch();
}


struct record *  del(struct record *start)  // delete haven correct it yet
{
	char name;
	struct record *curr;
	printf("\n Enter the name to delete:");
	gets(name);fflush(stdin);
	curr=start;
	if(strcmp(curr->name,name)==0)
		{
			if(start==NULL)
				{
				start=(struct record *) malloc(sizeof(struct record));
				strcpy(start->name,"   ");
				start->next=NULL;
				}
			printf("\n\n\t Deletion successful!");
		}
	while(curr)
	{
		
		if(strcmp(curr->next->name,name)==0)
		{
			curr->next=curr->next->next;
			printf("\n Deletion successful !");
		}
		else
			curr=curr->next;
	}
	return start;
}

view(struct record *start)
{
	struct record *curr;
	curr=start;
	while(curr != NULL)
	{
		printf("\n %s \n ",curr->name);
		curr=curr->next;
		getch();
	}
	printf("\n\n\t No more records !");

}

 struct record *append(struct record *start)
{
		struct record *curr;
		char name[30];
		static int flag;
		printf("\n Enter the name :");
		gets(name);fflush(stdin);
	
		if(flag==0 || strcmp(start->name," ")==0)
		{
			strcpy(start->name,name);
			start->next=NULL;
			flag =1 ;
			getch();
		}
		else
		{
            
			curr=start;
			while(curr != NULL)
			{
                       if( curr->next == NULL)
                       {
    			            curr->next=(struct record *) malloc(sizeof(struct record));
                            curr=curr->next;
    			            strcpy(curr->name,name);
    			            curr->next=NULL;
    			            curr = curr->next ;
                        }
                        else
                        {curr = curr->next ; }
        }
		}
		printf("\n\n\t Append successful!");
		return start;
	getch();
}

Can guide me where is the insertion went wrong? Still cannot insert before the first node @.@

**kekewong** · 10-09-2009

LOL, finally i fix it !!!! XD

Code:

#include<stdio.h>
#include<stdlib.h>
#include<string.h>

struct record
{
	char name[30];
	struct record *next;
};

void main()
{
	int choice;
	char ans;

    struct record *insert(struct record *), *append(struct record *);  //prototype\
     void view(struct record *);
	struct record *del(struct record *); //prototype
	struct record *start;

	
	start=(struct record *)malloc(sizeof(struct record));
	start->next=NULL;
    
	do
	{
		system("cls");
		printf("\n\n 1. Insert");
		printf("\n 2. Deletion");
		printf("\n 3. View");	
		printf("\n 4. Append");
		printf("\n 5. EXIT");
		printf("\n\n Choice:");
		scanf("%d",&choice);fflush(stdin);

		switch(choice)
		{
		case 1:
			start = insert(start);
			break;
		case 2:
			del(start);
			break;
		case 3:
			view(start);
			break;
		case 4:
			start = append(start);
			break;
		case 5:
			 exit(0);
		default:
			printf("\n Invalid Choice ");
		}
	}while(choice!=99);
}


 struct record *insert( struct record *start) 
{
	char name[30],name1[30],flag=' ';
	struct record *temp,*curr, *prev;
	curr=start;  
	printf("\n Enter name to insert :");
	gets(name);fflush(stdin);
	printf("\n Enter the name before which to insert:");
	gets(name1);fflush(stdin);
	
	while(curr != NULL && flag == ' ')  
	{       
          if(strcmp(curr->name,name1)== 0)
          {
                         flag='*';
                         temp=(struct record *) malloc(sizeof(struct record));
                       	 strcpy(temp->name,name);
                         temp->next = curr;
                         curr = temp;
                         printf("\nInsertion done !");
                          getch();
         	             return curr;
                      	 break;
          }
          
		else if(strcmp(curr->next->name,name1)== 0)
		            {	flag='*';
            			temp=(struct record *) malloc(sizeof(struct record));
                        prev  = curr;
            			strcpy(temp->name,name);
            			temp->next = prev->next;
            			prev->next =temp;
            			 getch();
            			printf("\n Insertion done !");
            				return start;
            			break;
		}
		else
			curr=curr->next;
	}
	if(flag==' ')
		printf("\n Record not found !");
		getch();
}


struct record *  del(struct record *start) // HAVEN FIX DELETE FUNCTION
{
	char name;
	struct record *curr;
	printf("\n Enter the name to delete:");
	gets(name);fflush(stdin);
	curr=start;
	if(strcmp(curr->name,name)==0)
		{
			if(start==NULL)
				{
				start=(struct record *) malloc(sizeof(struct record));
				strcpy(start->name,"   ");
				start->next=NULL;
				}
			printf("\n\n\t Deletion successful!");
		}
	while(curr)
	{
		
		if(strcmp(curr->next->name,name)==0)
		{
			curr->next=curr->next->next;
			printf("\n Deletion successful !");
		}
		else
			curr=curr->next;
	}
	return start;
}

view(struct record *start)
{
	struct record *curr;
	curr=start;
	while(curr != NULL)
	{
		printf("\n %s \n ",curr->name);
		curr=curr->next;
		getch();
	}
	printf("\n\n\t No more records !");

}

 struct record *append(struct record *start)
{
		struct record *curr;
		char name[30];
		static int flag;
		printf("\n Enter the name :");
		gets(name);fflush(stdin);
	
		if(flag==0 || strcmp(start->name," ")==0)
		{
			strcpy(start->name,name);
			start->next=NULL;
			flag =1 ;
			getch();
		}
		else
		{
            
			curr=start;
			while(curr != NULL)
			{
                       if( curr->next == NULL)
                       {
    			            curr->next=(struct record *) malloc(sizeof(struct record));
                            curr=curr->next;
    			            strcpy(curr->name,name);
    			            curr->next=NULL;
    			            curr = curr->next ;
                        }
                        else
                        {curr = curr->next ; }
        }
		}
		printf("\n\n\t Append successful!");
		return start;
	getch();
}

But i still got problem , refering to tabstop says, i also can use

Code:

void insert(struct record **)

Can teach me how to write? i am kind of confusing of two "**" in the same time @.@ ,

**kekewong** · 10-09-2009

LOL, finally i fix it !!!! XD

Code:

#include<stdio.h>
#include<stdlib.h>
#include<string.h>

struct record
{
	char name[30];
	struct record *next;
};

void main()
{
	int choice;
	char ans;

    struct record *insert(struct record *), *append(struct record *);  //prototype\
     void view(struct record *);
	struct record *del(struct record *); //prototype
	struct record *start;

	
	start=(struct record *)malloc(sizeof(struct record));
	start->next=NULL;
    
	do
	{
		system("cls");
		printf("\n\n 1. Insert");
		printf("\n 2. Deletion");
		printf("\n 3. View");	
		printf("\n 4. Append");
		printf("\n 5. EXIT");
		printf("\n\n Choice:");
		scanf("%d",&choice);fflush(stdin);

		switch(choice)
		{
		case 1:
			start = insert(start);
			break;
		case 2:
			del(start);
			break;
		case 3:
			view(start);
			break;
		case 4:
			start = append(start);
			break;
		case 5:
			 exit(0);
		default:
			printf("\n Invalid Choice ");
		}
	}while(choice!=99);
}


 struct record *insert( struct record *start) 
{
	char name[30],name1[30],flag=' ';
	struct record *temp,*curr, *prev;
	curr=start;  
	printf("\n Enter name to insert :");
	gets(name);fflush(stdin);
	printf("\n Enter the name before which to insert:");
	gets(name1);fflush(stdin);
	
	while(curr != NULL && flag == ' ')  
	{       
          if(strcmp(curr->name,name1)== 0)
          {
                         flag='*';
                         temp=(struct record *) malloc(sizeof(struct record));
                       	 strcpy(temp->name,name);
                         temp->next = curr;
                         curr = temp;
                         printf("\nInsertion done !");
                          getch();
         	             return curr;
                      	 break;
          }
          
		else if(strcmp(curr->next->name,name1)== 0)
		            {	flag='*';
            			temp=(struct record *) malloc(sizeof(struct record));
                        prev  = curr;
            			strcpy(temp->name,name);
            			temp->next = prev->next;
            			prev->next =temp;
            			 getch();
            			printf("\n Insertion done !");
            				return start;
            			break;
		}
		else
			curr=curr->next;
	}
	if(flag==' ')
		printf("\n Record not found !");
		getch();
}


struct record *  del(struct record *start) // HAVEN FIX DELETE FUNCTION
{
	char name;
	struct record *curr;
	printf("\n Enter the name to delete:");
	gets(name);fflush(stdin);
	curr=start;
	if(strcmp(curr->name,name)==0)
		{
			if(start==NULL)
				{
				start=(struct record *) malloc(sizeof(struct record));
				strcpy(start->name,"   ");
				start->next=NULL;
				}
			printf("\n\n\t Deletion successful!");
		}
	while(curr)
	{
		
		if(strcmp(curr->next->name,name)==0)
		{
			curr->next=curr->next->next;
			printf("\n Deletion successful !");
		}
		else
			curr=curr->next;
	}
	return start;
}

view(struct record *start)
{
	struct record *curr;
	curr=start;
	while(curr != NULL)
	{
		printf("\n %s \n ",curr->name);
		curr=curr->next;
		getch();
	}
	printf("\n\n\t No more records !");

}

 struct record *append(struct record *start)
{
		struct record *curr;
		char name[30];
		static int flag;
		printf("\n Enter the name :");
		gets(name);fflush(stdin);
	
		if(flag==0 || strcmp(start->name," ")==0)
		{
			strcpy(start->name,name);
			start->next=NULL;
			flag =1 ;
			getch();
		}
		else
		{
            
			curr=start;
			while(curr != NULL)
			{
                       if( curr->next == NULL)
                       {
    			            curr->next=(struct record *) malloc(sizeof(struct record));
                            curr=curr->next;
    			            strcpy(curr->name,name);
    			            curr->next=NULL;
    			            curr = curr->next ;
                        }
                        else
                        {curr = curr->next ; }
        }
		}
		printf("\n\n\t Append successful!");
		return start;
	getch();
}

Thanks alot TabStop

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