โค้ด แบบนี้ ทำงานยังไง หรอครับ อธิบายให้ที

#include<stdio.h>

#include<conio.h>

#include<string.h>

#include<process.h>

#include<stdlib.h>

#include<dos.h>

struct contact

{

    long ph;

    char name[20];
    char add[20];
    char email[30];

} list;

char query[20],name[20];

FILE *fp, *ft;

int i,n,ch,l,found;

int main()

{

main:

    system("cls");    /* Main menu  */

    printf("\n\t **** Welcome to Contact Management System ****");

    printf("\n\n\n\t\t\tMAIN MENU\n\t\t=====================\n\t\t[1] Add a new Contact\n\t\t[2] List all Contacts\n\t\t[3] Search for contact\n\t\t[4] Delete a Contact\n\t\t[0] Exit\n\t\t=================\n\t\t");

    printf("Enter the choice:");

    scanf("%d",&ch);

    switch(ch)

    {

    case 0:

        printf("\n\n\t\tAre you sure you want to exit?");

        break;

        /* Add new contacts */

    case 1:

        system("cls");

        fp=fopen("contact.txt","a");


        {
            fflush(stdin);

            printf("To exit enter blank space in the name input\nName (Use identical):");

            scanf("%[^\n]",&list.name);

            if(stricmp(list.name,"")==0 || stricmp(list.name," ")==0)

                break;

            fflush(stdin);

            printf("Phone:");

            scanf("%ld",&list.ph);

            fflush(stdin);

            printf("address:");

            scanf("%[^\n]",&list.add);

            fflush(stdin);

            printf("email address:");

            gets(list.email);

            printf("\n");

            fwrite(&list,sizeof(list),1,fp);

        }

        fclose(fp);

        break;

        /* list of contacts  */

    case 2:

        system("cls");

        printf("\n\t\t================================\n\t\t\tLIST OF CONTACTS\n\t\t================================\n\nName\t\tPhone No\t    Address\t\tE-mail ad.\n=================================================================\n\n");

        for(i=97; i<=122; i=i+1)
        {

            fp=fopen("contact.txt","r");

            fflush(stdin);

            found=0;

            while(fread(&list,sizeof(list),1,fp)==1)

            {

                if(list.name[0]==i || list.name[0]==i-32)

                {

                    printf("\nName\t: %s\nPhone\t: %ld\nAddress\t: %s\nEmail\t: %s\n",list.name,

                           list.ph,list.add,list.email);

                    found++;

                }

            }

            if(found!=0)

            {
                printf("=========================================================== [%c]-(%d)\n\n",i-32,found);

                getch();
            }

            fclose(fp);

        }

        break;

        /* search contacts */

    case 3:

        system("cls");

        do

        {

            found=0;

            printf("\n\n\t..::CONTACT SEARCH\n\t===========================\n\t..::Name of contact to search: ");

            fflush(stdin);

            scanf("%[^\n]",&query);

            l=strlen(query);

            fp=fopen("contact.txt","r");

            system("cls");

            printf("\n\n..::Search result for '%s' \n===================================================\n",query);

            while(fread(&list,sizeof(list),1,fp)==1)

            {

                for(i=0; i<=l; i++)

                    name=list.name;

                name[l]='\0';

                if(stricmp(name,query)==0)

                {

                    printf("\n..::Name\t: %s\n..:hone\t: %ld\n..::Address\t: %s\n..::Email\t: %s\n",list.name,list.ph,list.add,list.email);

                    found++;

                    if (found%4==0)

                    {

                        printf("..:ress any key to continue...");

                        getch();

                    }

                }

            }

            if(found==0)

                printf("\n..::No match found!");

            else

                printf("\n..::%d match(s) found!",found);

            fclose(fp);

            printf("\n ..::Try again?\n\n\t[1] Yes\t\t[0] No\n\t");

            scanf("%d",&ch);

        }
        while(ch==1);

        break;

        /*delete contacts*/

    case 4:

        system("cls");

        fflush(stdin);

        printf("\n\n\t..:ELETE A CONTACT\n\t==========================\n\t..::Enter the name of contact to delete:");

        scanf("%[^\n]",&name);

        fp=fopen("contact.txt","r");

        ft=fopen("temp.txt","w");

        while(fread(&list,sizeof(list),1,fp)!=0)

            if (stricmp(name,list.name)!=0)

                fwrite(&list,sizeof(list),1,ft);

        fclose(fp);

        fclose(ft);

        remove("contact.txt");
        rename("temp.txt","contact.txt");
        break;
    default:
        printf("Invalid choice");
        break;
    }
    printf("\n\n\n..::Enter the Choice:\n\n\t[1] Main Menu\t\t[0] Exit\n");
    scanf("%d",&ch);
    switch (ch)
    {
    case 1:
        goto main;
    case 0:
        break;
    default:
        printf("Invalid choice");
        break;
    }
    return 0;
}
ผมสนใจแล้วอยากจะศึกษา ภาษา C ครับไม่รู้จะเริ่มจากตรงไหน ก็ลองๆ เซิด อากูว่าตัวนี้ ใช้ทำอะไร ใช้ยังไง แต่ก็ยัง งงกับการทำงานครับ
ผมพึ่งจะขึ้น ม.6 เลยสนใจ แต่ความรู้ยังไม่ถึงขนาดนั้น วอนผู้รู้ เช่น ทำไม case 2 ต้อง i=97 i<122 แล้วเป็นยังอื่นได้ไหม ประมาณนี้ครับ