Программа, которая реализует с файлом последовательного доступа некоторые операции: создание, ввод, вывод и поиск по значению ключевого поля

Проблема возникает, когда я:

1)пытаюсь сделать удаление информации по ключевому полю(данные из файла просто удаляются);

2)не получается реализовать поиск информации по ключевому полю.

Ключевое поле - значение code в структуре Research_station.

Информация - все объекты в структуре Research_station (code, name, number_of_cultures).

Вот весь код(извините, что такой огромной, но пришлось вывести весь для общей картины):

    #include <stdio.h>
    #include <stdlib.h>
    #include <string.h>
    #define STRING 255

    typedef struct {
    int code;
    char name[STRING];
    int number_of_cultures;
    } Research_station;

    void Creating(Research_station *H, int n) {

    FILE *fp;
    fp=fopen("test.txt", "w");
    if(fp==NULL)
    {
        printf("Can't create file");
        getch();
        exit(1);
    }
    printf("\n\tHow many research stations you want to enter: ");
    scanf("%d",&n);
    for(int i=0; i<n; i++)
    {
        printf("\n****************************************");
        printf("\nEnter research station code: ");
        scanf("%d",&(H+i)->code);
        printf("\nEnter research station name: ");
        scanf("%s",&(H+i)->name);
        printf("\nEnter the number of cultures of the research station: ");
        scanf("%d",&(H+i)->number_of_cultures);
        fprintf(fp,"Research station code: %d \nResearch station name: %s \nThe number of cultures of the research station: %d \n", (H+i)->code, (H+i)->name, (H+i)->number_of_cultures);
    }
    fclose(fp);
    }

    void Outputting(Research_station *H, int n) {
    
    FILE *fp;
    fp=fopen("test.txt","r");
    if(fp==NULL)
    {
        printf("Can't read file");
        getch();
        exit(1);
    }

    char m[STRING];
    printf("\n\tHow many research stations you entered: ");
    scanf("%d", &n);
    for(int i=0; i<n*3; i++){
        fgets(m, STRING, fp);
        printf("%s", m);
    }
    fclose(fp);
    }

    void Searching() {

    FILE *fp;
    fp=fopen("test.txt", "r+");
    if(fp==NULL)
    {
        printf("Can't create file");
        getch();
        exit(1);
    }

    int search_with_code;
    printf("\nEnter the research station code: ");
    scanf("%d",&search_with_code);
    }

    void Adding(Research_station *H, int n, int n1) {

    FILE *fp;
    fp=fopen("test.txt", "a");
    if(fp==NULL)
    {
        printf("Can't create file");
        getch();
        exit(1);
    }

    for(int i=0; i<n1; i++)
    {
        printf("\n****************************************\n");
        printf("\nEnter research station code: ");
        scanf("%d",&(H+i)->code);
        printf("\nEnter research station name: ");
        scanf("%s",&(H+i)->name);
        printf("\nEnter the number of cultures of the research station: ");
        scanf("%d",&(H+i)->number_of_cultures);
        fprintf(fp,"Research station code: %d \nResearch station name: %s \nThe number of cultures of the research station: %d \n", (H+i)->code, (H+i)->name, (H+i)->number_of_cultures);
    }
    fclose(fp);
    }

    void Deleting(Research_station *H, int n) {

    FILE *fp;
    fp=fopen("test.txt", "w+");
    if(fp==NULL)
    {
        printf("Can't create file");
        getch();
        exit(1);
    }

    int delete_with_code;
    printf("\nEnter the research station code: ");
    scanf("%d",&delete_with_code);

    for(int i = 0; i<n; i++){
        if(delete_with_code == (H+i)->code) continue;
        fprintf(fp,"Research station code: %d \nResearch station name: %s \nThe number of cultures of the research station: %d \n",(H+i)->code,(H+i)->name,(H+i)->number_of_cultures);
    }
    fclose(fp);
    }

    void print_menu() {

    system("cls");
    printf("What do you want to do?\n");
    printf("1. Create a file and enter information\n");
    printf("2. Output of all information (from the file)\n");
    printf("3. Search for information from a file by key field\n");
    printf("4. Adding information to a file\n");
    printf("5. Delete information from a file by key field\n");
    printf("6. Exit the program\n");
    printf("> ");
    }

    int get_variant(int count) {

    int variant;
    char s[100];
    scanf("%s", s);

    while (sscanf(s, "%d", &variant) != 1 || variant < 1 || variant > count) 
    {
        printf("Incorrect input. Try again: ");
        scanf("%s", s);
    }

    return variant;
    }

    int main(void) {

    Research_station *pH;
    Research_station  H;
    pH=&H;

    int n, n1, c;
    int variant;

    do {
        print_menu();

        variant = get_variant(6);

        switch (variant) {
            case 1:
                Creating(pH, n);
                break;

            case 2:
                Outputting(pH, n);
                break;

            case 3:
                Searching();
                break;

            case 4:
                printf("\n\tHow many research stations you want to add: ");
                scanf("%d",&n1);
                Adding(pH, n, n1);
                n+=n1;
                break;

            case 5:
                Deleting(pH, n);
                n-=1;
                break;
    }

    if (variant != 6)
        system("pause");
    } while (variant != 6);

    return 0;
    }