#define _CRT_SECURE_NO_WARNINGS // ワーニングを無効にする

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

#define MAX_CHAR_PER_LINE 256

int main() {
    FILE* inputFile, * outputFile;
    char tempFileName[] = "temp.txt";
    char inputFileName[] = "input.txt";
    char outputFileName[] = "output.txt";
    char newLine[] = "This is the new first line.\n";
    char buffer[MAX_CHAR_PER_LINE];
    int lineNumber = 0;

    // Open the input file for reading
    if (fopen_s(&inputFile, inputFileName, "r") != 0) {
        perror("Error opening the file");
        return 1;
    }

    // Open the temporary file for writing
    if (fopen_s(&outputFile, tempFileName, "w") != 0) {
        perror("Error opening temporary file");
        return 1;
    }

    // Write the new first line to the temporary file
    fputs(newLine, outputFile);

    // Read each line from the input file and write to the temporary file, excluding the line to be deleted
    while (fgets(buffer, MAX_CHAR_PER_LINE, inputFile) != NULL) {
        lineNumber++;
        // Skip the line to be deleted (in this example, we delete line 2)
        if (lineNumber == 2) {
            continue;
        }
        fputs(buffer, outputFile);
    }

    // Close the input and temporary files
    fclose(inputFile);
    fclose(outputFile);

    // Remove the original file
    if (remove(inputFileName) != 0) {
        perror("Error deleting the file");
        return 1;
    }

    // Rename the temporary file to the original file name
    if (rename(tempFileName, outputFileName) != 0) {
        perror("Error renaming the file");
        return 1;
    }

    printf("Operation successful.\n");
    return 0;
}