阅读文本文件。如果输入相同，请打印“已存在”

Question

这是文本文件数据：

值78,2,98是productID。

78 MINERALWATER 123 345.00
2 RAYBAN 2 450.00
98 ADIDASWATCH 19 200.00

如果用户输入的输入与上面的productID相同。我怎么打印，“产品已经存在！”

以下是我在int addProduct()中已经改变的代码部分。

    printf("Enter product ID : ");
    scanf(" %d", &a.id);

    productID = a.id;

    fp = fopen("inventory.txt","r");
    while(fscanf(fp, "%d %s %d %f", &a.id, a.name, &a.quantity, &a.price)==4)
        {
            ///The Output Came From Text File Must Be Same As User Instructed
            if(a.id == productID)
            {
            printf("The item already exist!");
            }
            else{
                 gotoxy(22,10);
    printf("Enter product name : ");
    scanf(" %s", a.name);

    gotoxy(22,12);
    printf("Enter product quantity : ");
    scanf(" %d", &a.quantity);

    gotoxy(22,14);
    printf("Enter product price : ");
    scanf(" %f", &a.price);


    gotoxy(22,17);
    ///Store @ Write Product Data Inside FP Text File
    fprintf(fp, "%d %s %d %f\n\n", a.id, a.name, a.quantity, a.price);

    printf("Record saved!\n\n");

            }
        }

用户输入值2并存储在a.id。然后，编译器扫描整个文件，如果a.id = productID，则打印项已经存在。否则，继续添加新产品。

但是，它失败了。编译器继续添加数据，尽管用户输入值2和文本文件变为：

78 MINERALWATER 123 345.00
2 RAYBAN 2 450.00
98 ADIDASWATCH 19 200.00
2 NEWITEM 4 219.00

如果存在相同的productID，那么这是我的完整代码而不会出现循环争议：兴趣点在int addProduct()

#include <stdio.h>
#include <stdlib.h>
#include <windows.h>
#include <ctype.h>
#include <conio.h>

///Function Prototype
void gotoxy( int column, int line );
int main();
int addProduct();
int displayProduct();
int searchProduct();
int reorderProduct();
int updateProduct();

///Global Variables
struct product
{
    int quantity, reorder, i, id;
    char name[20];
    float price;
};

COORD coord = {0, 0};

///GotoXY Function
void gotoxy (int x, int y)
{
coord.X = x; coord.Y = y;

SetConsoleCursorPosition(GetStdHandle(STD_OUTPUT_HANDLE), coord);
}

///Main Function
int main()
{
    int choice;

        ///GotoXY Output
        gotoxy(17,5);
        printf("\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2 SYZ INVENTORY PROGRAM \xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2");

        gotoxy(17,20);
        printf("\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2");

        ///Menu Display
        gotoxy(22,8);
        printf("1. Add Product\n\n");

        gotoxy(22,10);
        printf("2. Display Product\n\n");

        gotoxy(22,12);
        printf("3. Search Product\n\n");

        gotoxy(22,14);
        printf("4. Reorder Level of Product\n\n");

        gotoxy(22,16);
        printf("5. Update Product\n\n");

        gotoxy(22,18);
        printf("6. Exit\n\n");

        ///Choice Input
        gotoxy(22,22);
        printf("Please Enter Your Choice : ");
        scanf(" %d", &choice);

        ///Choice Using Switch Case
        switch(choice)
            {
            case 1 :    addProduct();
                        break;

            case 2 :    displayProduct();
                        break;

            case 3 :    searchProduct();
                        break;

            case 4 :    reorderProduct();
                        break;

            case 5 :    updateProduct();
                        break;

            case 6 :    break;

            default :   system("cls");
                        main();

            }
return (0);
}


///Add Product Function
int addProduct()
{
    ///File Pointer
    FILE * fp;
    int number;
    char checker;
    struct product a;

    ///Clear Screen On Command Prompt
    system("cls");

    ///FP Text File is Open. A = Append
    fp = fopen("inventory.txt","a+t");

        ///Do-While Loop For Product Input
        do
        {
        system("cls");

        ///GotoXY Output
        gotoxy(17,5);
        printf("\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2 SYZ INVENTORY PROGRAM \xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2");

        gotoxy(17,20);
        printf("\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2");

        ///4 Input Of Add Product | Product ID | Product Name | Product Quantity | Product Price |
        gotoxy(22,8);
        printf("Enter product ID : ");
        scanf(" %d", &a.id);

        gotoxy(22,10);
        printf("Enter product name : ");
        scanf(" %s", a.name);

        gotoxy(22,12);
        printf("Enter product quantity : ");
        scanf(" %d", &a.quantity);

        gotoxy(22,14);
        printf("Enter product price : ");
        scanf(" %f", &a.price);


        gotoxy(22,17);
        ///Store @ Write Product Data Inside FP Text File
        fprintf(fp, "%d %s %d %f\n\n", a.id, a.name, a.quantity, a.price);

        printf("Record saved!\n\n");

        ///Close FP Text File
        fclose(fp);


        ///Choice Input For User Enter New Product Or Back To Main
        gotoxy(22,22);
        printf("Do you want to enter new product? Y / N : ");

        scanf(" %c", &checker);

        ///Change To Uppercase, If User Enter Lowercase Character
        checker = toupper(checker);

        system("cls");
        }
        ///If Checker Input is Y @ Yes : Continue Loop Adding Product
        while(checker=='Y');

            ///If Checker Input Is N @ No : Back To Main
            if(checker == 'N')
                {
                main();
                }

            else
            {
                do
                {
                system("cls");

                ///GotoXY Output
                gotoxy(17,5);
                printf("\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2 SYZ INVENTORY PROGRAM \xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2");

                gotoxy(17,20);
                printf("\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2");

                gotoxy(18,8);
                printf(">>> Wrong Input! Please Enter Y Or N Only! <<<");

                gotoxy(19,12);
                printf("Do You Want To Enter New Product? Y / N : ");
                scanf(" %c", &checker);

                ///Change To Uppercase, If User Enter Lowercase Character
                checker = toupper(checker);
                }
                ///Keep On Looping If User Enter Other Than Y Or N.
                while(checker != 'Y' && checker != 'N');

                ///If Input Y : Add Product
                if(checker == 'Y')  {   addProduct();  }

                ///If Input N : Back To Main
                if(checker == 'N')  {   system("cls");
                                        main();
                                    }

            }

return(0);
}


///Display Product Function
int displayProduct()
{
    ///File Pointer
    FILE * fp;

    struct product a;
    system("cls");

    ///FP Text File is Open. R = Read Only
    fp = fopen("inventory.txt","r");

        ///GotoXY Output
        gotoxy(17,5);
        printf("\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2 SYZ INVENTORY PROGRAM \xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2");

        gotoxy(5,6);
        printf("======================================================================");

        ///Table Title
        gotoxy(5,7);
        printf("Product ID\t\t Product Name\t\t Quantity\t Unit Price\n");

        gotoxy(5,8);
        printf("======================================================================");

        ///Content Of Text File Is Read And Store Into Variables
        gotoxy(0,10);
        while(fscanf(fp, "%d %s %d %f", &a.id, a.name, &a.quantity, &a.price)==4)
        {
        ///List Of Product From Text File Is Display On Command Prompt
        printf("\t%-10d\t %-12s\t\t %8d\t %8.2f\n\n", a.id, a.name, a.quantity, a.price);
        }

        ///Close FP Text File
        fclose(fp);

        ///GotoXY Output
        printf("\t\t \xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2");

        printf("\n\n\t\t    >> Press any key to return to Main Menu <<");

    getch();
    system("cls");

    ///Back To Main Function
    main();

return (0);
}



int searchProduct()
{
    ///File Pointer
    FILE * fp;

    system("cls");
    struct product a;
    int productID;

    ///FP Text File is Open. R = Read Only
    fp = fopen("inventory.txt","r");

        ///GotoXY Output
        gotoxy(17,5);
        printf("\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2 SYZ INVENTORY PROGRAM \xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2");

        gotoxy(17,20);
        printf("\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2");

        ///Input Product ID Want To Search
        gotoxy(22,8);
        printf("Please enter product ID : ");
        scanf(" %d", &productID);

        gotoxy(5,10);
        printf("======================================================================");

        ///Table Title
        gotoxy(5,12);
        printf("Product ID\t\t Product Name\t\t Quantity\t Unit Price\n");

        gotoxy(5,14);
        printf("======================================================================");


            gotoxy(0,16);
            ///Content Of Text File Is Read And Store Into Variables
            while(fscanf(fp, "%d %s %d %f", &a.id, a.name, &a.quantity, &a.price)==4)
            {
                ///The Output Came From Text File Must Be Same As User Instructed
                if(a.id == productID)
                {
                printf("\t%-10d\t %-12s\t\t %8d\t %8.2f\n\n", a.id, a.name, a.quantity, a.price);
                }
            }

        ///Close FP Text File
        fclose(fp);
        gotoxy(17,20);
        printf("\n\n\t\t    >> Press any key to return to Main Menu <<");

    getch();
    system("cls");
    main();

return(0);
}


int reorderProduct()
{
    ///File Pointer
    FILE * fp;

    system("cls");
    struct product a;
    int productQuantity;

    ///FP Text File is Open. R = Read Only
    fp = fopen("inventory.txt","r");

        ///GotoXY Output
        gotoxy(17,5);
        printf("\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2 SYZ INVENTORY PROGRAM \xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2");

        ///Input Minimum Product Quantity
        gotoxy(22,8);
        printf("Please enter minimum reorder level : ");
        scanf(" %d", &productQuantity);

        gotoxy(5,10);
        printf("======================================================================");

        ///Table Title
        gotoxy(5,12);
        printf("Product ID\t\t Product Name\t\t Quantity\t Unit Price\n");

        gotoxy(5,14);
        printf("======================================================================");

        gotoxy(0,16);
        ///Content Of Text File Is Read And Store Into Variables
        while(fscanf(fp, "%d %s %d %f", &a.id, a.name, &a.quantity, &a.price)==4)
        {
            if(productQuantity >= a.quantity)
            {
            ///The Output Came From Text File Must Be Greater Or Equal As User Instructed (Item Need To Be Reorder)
            printf("\t%-10d\t %-12s\t\t %8d\t %8.2f\n\n", a.id, a.name, a.quantity, a.price);
            }
        }

        ///Close FP Text File
        fclose(fp);

        ///GotoXY Output
        printf("\t\t \xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2");

        printf("\n\n\t\t    >> Press any key to return to Main Menu <<");

    getch();
    system("cls");
    main();

return (0);
}



int updateProduct()
{
    ///File Pointer
    FILE *fp, *fp2;

    system("cls");
    struct product a;
    int productID;

    ///FP Text File is Open. R = Read Only
    fp = fopen("inventory.txt","r");
    rewind(fp);

    ///FP Text File is Open. R = Read Only
    fp2 = fopen("temporary.txt" ,"a");

        ///GotoXY Output
        gotoxy(17,5);
        printf("\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2 SYZ INVENTORY PROGRAM \xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2");

        gotoxy(17,20);
        printf("\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2\xB2");

        ///Input Product ID To Be Update
        gotoxy(22,8);
        printf("Enter product ID : ");
        scanf(" %d", &productID);

        ///Content Of Text File FP Is Read
        while (!feof(fp))
        {
        ///Content Is Store Into Variables
        fscanf(fp, "%d %s %d %f", &a.id, a.name, &a.quantity, &a.price);

            if (feof(fp)) { continue; }

            if (a.id == productID) continue;

            fprintf(fp2, "%d %s %d %f\n\n", a.id, a.name, a.quantity, a.price);

        }

        ///Close FP Text File
        fclose(fp);
        fclose(fp2);

        ///Inventory Text File Is Remove
        remove("inventory.txt");
        ///Temporary Text File Is Rename Into Inventory Text File
        rename("temporary.txt", "inventory.txt");

        ///FP Text File is Open. R = Append
        fp = fopen("inventory.txt","a+t");

        ///3 Input Of Add Product | Product Name | Product Quantity | Product Price |
        gotoxy(22,10);
        printf("Enter product name : ");
        scanf(" %s", a.name);

        gotoxy(22,12);
        printf("Enter product quantity : ");
        scanf(" %d", &a.quantity);

        gotoxy(22,14);
        printf("Enter product price : ");
        scanf(" %f", &a.price);

        gotoxy(22,17);
        ///Store @ Write Product Data Inside FP Text File
        fprintf(fp, "%d %s %d %f\n\n", productID, a.name, a.quantity, a.price);
        printf("Record saved!\n\n");

        ///Close FP Text File
        fclose(fp);

        printf("\n\n\t\t    >> Press any key to return to Main Menu <<");

    getch();
    system("cls");
    main();

return(0);
}