//THIS FUNCTION ADDS A NEW ENTRY TO THE phonebook_list
void insert(void){
    //variables
    int flag=0, length=0, menu=0, i=0, check=0;
    NODE *p,*q, *temp;

    //USER MUST ENTER FIRST NAME ONLY FOR ADDITION TO PHONEBOOK
    printf("\nPlease insert the <First Name> of the entry you would like to add not separated by a space.\n");
    if((temp=(NODE *)malloc(sizeof(NODE))) == (NODE *)NULL)
    {
        printf("Memory could not be allocated! Returning to menu...\n\n");
        return;
    }
    scanf("%s", temp->name);
    //check if name is too long for the array IF IT IS PROMPTS USER TO RE ENTER SHORTER NAME
    while(flag==0)
    {                                    
        length=strlen(temp->name);
        if(length<50){
            for(i=0;i<length;i++)
                temp->name[i] = toupper(temp->name[i]);
            flag=1;
        }else{                    
            printf("\nName is too long! Please re-enter (less than 50 characters).\n");
            scanf("%s", temp->name);
            length=strlen(temp->name);
        }
    }
    //prompt user for telephone number
    printf("%s",temp->number);
    printf("\nPlease insert the telephone number in the following format XXXXXXXXXX.\n");
    scanf("%s", temp->number);
    flag=0;

    //check if number has the correct number of chars
    while(flag==0){
        length=strlen(temp->number);
        if(length==10){
            flag=1;
        }else{
            printf("\nThis is an invalid number. Please re-enter.\n");
            scanf("%s", temp->number);
            length=strlen(temp->number);
        }
    }
    printf("%s", head->name);
    //IF PHONEBOOK IS EMPTY THEN THE HEAD WILL BE A NULL POINTER AND TEMP NODE WILL BE ADDED
    if(head==NULL)
        {
        if((head=(NODE *)malloc(sizeof(NODE))) == (NODE*)NULL)
        {
            printf("Memory could not be allocated!\nReturning to menu...\n\n");
            return;
        }else{    
            strcpy(head->number,temp->number);
            strcpy(head->name,temp->name);
            head->next=tail;
            free(temp);
            printf("Entry successfully added.\n\n");
            return;
        }
    }else{
        //IF NEW NODE IS NOT THE FIRST ENTRY(NODE) IN PHONEBOOK(LIST) WILL LOOP THROUGH PHONEBOOK TO FIND CORRECT SPOT TO ADD
        p=head;
        printf("%s", p->name);
        while(p->next!=NULL)
        {
            //IF NAME IS ALREADY IN PHONEBOOK ERROR IS GIVEN AND PROGRAM RETURNS USER TO MAIN MENU
            if(strcmp(p->name,temp->name)==0)
            {
                printf("This name already exists in phonebook!\nReturning to menu...\n\n");
                return;
            //OTHERWISE THE WHILE LOOP WILL CONTINUE THROUGH LIST UNTIL IT FIND THE ADDITION THAT IS ALPHABETICALLY HIGHER
            //AND WILL ADD THAT NODE IN ITS CORRECT SPOT
            }else if(strcmp(p->name,temp->name)<0)
            {
                printf("\nTRUE\n");
                temp->next=p;
                temp->prev=p->prev;
                p->prev->next=temp;
                p->prev=temp;
                printf("Entry successfully added.\n\n");
                return;
            }
            p=p->next;
        }
        //IF NO NAME IS ALPHABETICALLY HIGHER, THAN IT SHOULD REACH THE LAST NODE AND WILL BE ADDED TO THE END OF THE PHONEBOOK(LIST)
        if(p->next==NULL)
        {
            if((temp=(NODE *)malloc(sizeof(NODE))) == (NODE *)NULL)
            {
                printf("Memory could not be allocated!\nReturning to menu...\n\n");
                return;
            }
            temp->next=tail;
            temp->prev=q;
            q->next=temp;
            free(temp);
            printf("Entry successfully added.\n\n");
            return;
        }
    }
}