task on a binary file on C

Question

I cannot understand why there is no record of the result in the G.bin file the task condition is to write part of the line before or after 0 in the second file you need to write down the part where the amount is greater.

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

int main()
{
    FILE* fa;
    errno_t err = fopen_s(&fa, "F.bin", "wb");
    if (err != 0)
    {
        printf("Error opening file F.bin\n");
        return 1;
    }

    printf("Enter numbers:\n");

    int sum_before = 0;
    int sum_after = 0;
    int num;
    int zero_encountered = 0;
    char input[256];
    fgets(input, sizeof(input), stdin);

    size_t input_length = strlen(input);
    if (input[input_length - 1] == '\n')
    {
        input[input_length - 1] = '\0'; // Видалити символ нового рядка
    }

    fwrite(input, sizeof(char), strlen(input), fa);

    fclose(fa);

    char* token;
    char* nextToken = NULL;
    token = strtok_s(input, " ", &nextToken);

    while (token != NULL)
    {
        num = atoi(token);
        if (num == 0)
        {
            zero_encountered = 1;
        }
        if (!zero_encountered)
        {
            sum_before += num;
        }
        else
        {
            sum_after += num;
        }
        token = strtok_s(NULL, " ", &nextToken);
    }

    FILE* fb;
    err = fopen_s(&fb, "G.bin", "wb");
    if (err != 0)
    {
        printf("Error opening file G.bin\n");
        return 1;
    }

    if (sum_before > sum_after)
    {
        size_t part_length = strlen(input) - strlen(nextToken) - 1; // Обчислюємо довжину першої частини
        fwrite(input, sizeof(char), part_length, fb);
    }
    else
    {
        fwrite(nextToken, sizeof(char), strlen(nextToken), fb);
    }

    fclose(fb);

    printf("Результат успішно записано у файл G.bin\n");

    return 0;
}

data from the keyboard:

12 45 78 0 312 545 899 

data that should be in the G.bin file:

312 545 899 

Answer 1

Some highlights:

1. Don't use errno_t, strtok_s.
2. Still you have possible bugs here (I didn't fix all your bugs).
3. You need to do another checks if the user insert another 0's. In your case is just for one and only one zero.

Here is fixed code:

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

int main() {
    FILE* fa = fopen("F.bin", "wb");
    if (fa == NULL) {
        printf("Error opening file F.bin\n");
        return 1;
    }

    printf("Enter numbers:\n");

    int sum_before = 0;
    int sum_after = 0;
    int num;
    int zero_poped = 0;
    int zero_encountered = 0;
    char input[256];
    fgets(input, sizeof(input), stdin);

    size_t input_length = strlen(input);
    if (input[input_length - 1] == '\n') {
        input[input_length - 1] = '\0'; // Remove the newline character
    }

    fwrite(input, sizeof(char), strlen(input), fa);
    fclose(fa);

    // Split the input string manually
    int i = 0;
    while (input[i] != '\0') {
        int j = i;
        while (input[j] != ' ' && input[j] != '\0') {
            j++;
        }

        char number[10];
        strncpy(number, input + i, j - i);
        number[j - i] = '\0';
        num = atoi(number);

        if (num == 0) {
            zero_encountered = 1;
            zero_poped = j + 1;
        }
        if (!zero_encountered) {
            sum_before += num;
        } else {
            sum_after += num;
        }

        i = j + 1;
    }

    FILE* fb = fopen("G.bin", "wb");
    if (fb == NULL) {
        printf("Error opening file G.bin\n");
        return 1;
    }

    if (sum_before > sum_after) {
        fwrite(input, sizeof(char), zero_poped - 1, fb);
    } else {
        fwrite(input + zero_poped, sizeof(char), strlen(input) - zero_poped, fb); 
    }
    fclose(fb);

    printf("Result successfully written to G.bin\n");

    return 0;
}

Output (before bigger):

Enter numbers:   
8 2 0 1 1
Result successfully written to G.bin
In G.bin - 8 2

Output (after bigger):

Enter numbers:   
1 2 0 1 8
Result successfully written to G.bin
In G.bin - 1 8