💻 Unit 5 – Part C (Descriptive Q&A)

Write a C program to copy the contents from one file to another file and to merge two files.

This question has two parts. Here are the programs for both operations.

Program 1: Copy contents from one file to another

This program reads one file (e.g., source.txt) character by character and writes each character to a new file (destination.txt).

#include <stdio.h>
#include <stdlib.h> // For exit()

int main() {
    FILE *sourceFile, *destFile;
    char ch;

    // --- Create a dummy source file for testing ---
    sourceFile = fopen("source.txt", "w");
    if(sourceFile == NULL) {
        printf("Error creating source.txt\n");
        return 1;
    }
    fprintf(sourceFile, "This is the content\nof the source file.\nHello World!");
    fclose(sourceFile);
    // ---------------------------------------------

    // Open source file for reading
    sourceFile = fopen("source.txt", "r");
    if (sourceFile == NULL) {
        printf("Error: Could not open source file 'source.txt'\n");
        exit(1);
    }

    // Open destination file for writing
    destFile = fopen("destination.txt", "w");
    if (destFile == NULL) {
        printf("Error: Could not create destination file 'destination.txt'\n");
        fclose(sourceFile);
        exit(1);
    }

    // Read from source and write to destination, character by character
    while ((ch = fgetc(sourceFile)) != EOF) {
        fputc(ch, destFile);
    }

    printf("File copied successfully!\n");
    printf("Check 'destination.txt' for the copied content.\n");

    // Close both files
    fclose(sourceFile);
    fclose(destFile);

    return 0;
}

Program 2: Merge two files into a third file

This program reads the contents of file1.txt and appends them to merged.txt, then reads the contents of file2.txt and appends them to merged.txt.

#include <stdio.h>
#include <stdlib.h> // For exit()

int main() {
    FILE *file1, *file2, *mergedFile;
    char ch;

    // --- Create dummy file 1 ---
    file1 = fopen("file1.txt", "w");
    if(file1 == NULL) { printf("Error.\n"); return 1; }
    fprintf(file1, "Content from file 1.\nSecond line of file 1.\n");
    fclose(file1);

    // --- Create dummy file 2 ---
    file2 = fopen("file2.txt", "w");
    if(file2 == NULL) { printf("Error.\n"); return 1; }
    fprintf(file2, "Content from file 2.\nThis is the last line.\n");
    fclose(file2);
    // ---------------------------------

    // --- Open files for merging ---
    file1 = fopen("file1.txt", "r");
    file2 = fopen("file2.txt", "r");
    
    // Open merged file in "w" (write) mode to create it
    mergedFile = fopen("merged.txt", "w"); 

    if (file1 == NULL || file2 == NULL || mergedFile == NULL) {
        printf("Error opening one or more files!\n");
        exit(1);
    }

    // 1. Copy content from file1 to mergedFile
    while ((ch = fgetc(file1)) != EOF) {
        fputc(ch, mergedFile);
    }
    
    fprintf(mergedFile, "\n"); // Add a newline for separation

    // 2. Copy content from file2 to mergedFile
    while ((ch = fgetc(file2)) != EOF) {
        fputc(ch, mergedFile);
    }

    printf("Files merged successfully into 'merged.txt'!\n");

    // Close all files
    fclose(file1);
    fclose(file2);
    fclose(mergedFile);

    return 0;
}