Thread: I need help, deleting nodes!

I am trying to delete a node in a contact manager based on the users criteria.I can add contacts just fin and print them out but i cant delete them.Right now im working on deleting a contact based on its SSN but my program crashes when i try to do it.My deletion function is in bold.

Code:

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


enum SSN_ID_type
{
    SSN, ID
};
typedef union SSN_ID_u
{
    int SSN;
    int ID;
} SSN_or_ID;
typedef struct pnumber
{
    int area;
    int prefix;
    int suffix;
} phone_number;
typedef struct homeAddress
{
    
    char* street;
    char* zip_code;
    char* city;
    char* state;
}home_address;
typedef struct cs_node
{
    //int number_of_nodes;
    home_address address;
    int id;
    char* first;/* declaration of firstname string*/
    char* last;/* declaration of lastname string*/
    phone_number phone;
    enum SSN_ID_type type;
    SSN_or_ID SSN_ID;
    struct cs_node* next;
} contact;

contact *start_ptr=NULL;

char *get_string()/* the call string function for first and last name*/
{
    char a;
    char* string1;
    int counter = 1;
    string1 = (char*)malloc(sizeof(char));
 
    while(((a = getchar())!='\n') && counter != -1)
    {
        string1 =(char*) realloc(string1, sizeof(char)*counter);
        if(string1 == NULL)
        {
            counter =-1;
        }
        else
        {
            string1[counter -1]=a;
            counter++;
        }
    }
    if(counter != -1)
    {
        string1= (char*) realloc(string1, sizeof(char)*counter);
        string1[counter-1] = '\0';
    }
    return(string1);
 
}
void add_contact ()
  { contact *temp;   // Temporary pointers
     char input[100];
  
    temp = (contact*)malloc(sizeof(contact));

    char id_choice = 'A';
     // Reserve space for new node and fill it with data
    //temp = new contact;
     getchar();
     printf("Enter contacts first name: ");
     temp->first=get_string();
     printf("Enter contacts last name : ");
     temp->last=get_string();
  
     do
     {
  
    printf("S) Enter the social security number for this contact\n");
    printf("I) Enter the student ID for this contact\n");

    printf(">> ");
	fgets(input,sizeof(input), stdin);
	sscanf(input,"&#37;c",&id_choice);
    //scanf("%c", &id_choice);
    if(id_choice == 'S')
    {
    
     printf(">> social security number: ");
	fgets(input,sizeof(input), stdin);
	sscanf(input,"%d",&temp->SSN_ID.SSN);
     //scanf("%d",&temp->SSN_ID.SSN);
     temp->type=SSN;
    
    }
    else if(id_choice == 'I')
    {
  
    printf(">> ID: ");
    fgets(input,sizeof(input), stdin);
    sscanf(input,"%d",&temp->SSN_ID.ID);
    temp->type=ID;
        }
    else
    {
    printf("Let's try that again.\n");
    }
    } while(id_choice != 'S' && id_choice != 'I');

     // Set up link to this node
    printf("Enter the phone number of this person\n>> ");
	fgets(input,sizeof(input), stdin);
        sscanf(input,"%i-%i-%i",&temp->phone.area,
                &temp->phone.prefix,
                &temp->phone.suffix);
                
    temp->next=start_ptr;
    start_ptr=temp;
     //count->number_of_nodes++;
     return ;
  }


void display_contact(contact*temp)
{
    printf("Name: %s %s\n",temp->first,temp->last);
    if(temp->type==SSN){
      printf("SSN:%d\n",temp->SSN_ID.SSN);
    }
    else{
      printf("ID:%d\n",temp->SSN_ID.ID);
      }
    printf("Phone Number:%d-%d-%d\n",temp->phone.area,temp->phone.prefix,temp->phone.suffix);
  //  printf("Street:%s\nCity:%s\nState:%s\nZip Code:%s\n",temp->address.street,temp->address.city,temp->address.state,temp->address.zip_code);
}
//////****Delete function*******////////////////////////
void delete_contact()
{
        
    int sel,input;
    int input_a,input_p,input_r;
    
    contact *curr_ptr,*prev_ptr;// declares current pointer and previous pointer.
    prev_ptr = NULL; //sets previous pointer to null


    printf("\nDelete Options:\n 1)Social Security #\n 2)ID number\n 3)phone number\n");
    scanf("%d",&sel);
    for (curr_ptr = start_ptr;curr_ptr != NULL;prev_ptr = curr_ptr, curr_ptr = curr_ptr->next)
    {
    if(sel==1){
        printf("Enter contatcs SSN:\n");
        scanf("%d",&input);
        if (curr_ptr->SSN_ID.SSN == input){ //checks if input criteria matches a contacts
        if(start_ptr==curr_ptr && prev_ptr==NULL){//deletes contacts if its the head/start node
          start_ptr= curr_ptr->next;
          free(curr_ptr);
        }if(curr_ptr==prev_ptr->next && curr_ptr->next!=NULL){//deletes contact if its a middle node
               
                
               prev_ptr->next = curr_ptr->next; //previous nodes pointer skips the removed node
               free(curr_ptr); 
        }
        if(curr_ptr->next==NULL && prev_ptr->next==curr_ptr){//deletes contact if contats is the last node
             prev_ptr->next==NULL;
             }
             if(start_ptr=NULL){// deletes contact if its the only node
                             free(curr_ptr);   
                                }
             
             
}
 }
  }
   }

void display_contacts()
{
    contact* tmp_node=start_ptr;
    int i = 0;

    while(tmp_node != NULL){
        printf("%d) ", i);
    display_contact(tmp_node);
        tmp_node = tmp_node->next;
        i++;
    }
}

int main()
{
    int selection = 0;
    
    do {
        printf("\n1) Enter a new contact\n");/* Main menu- gives users selections*/
        printf("2) Display the contacts\n");
        printf("3) Delete a contact\n");
        printf("4) Quit\n");
        printf(">> ");

        scanf("%d", &selection);

        if(selection == 1)
        {
            add_contact();
        }
        else if(selection == 2)
        {
            display_contacts();
        }
        
    else if(selection==3)
        {
        delete_contact();
    } 
        else if(selection != 4)
        {
    printf("Quit.\n\n");
        }

    } while(selection != 5);
    return 0;
}