`luc093.c`¶

Problem Statement

Update Master file (Roll, Name) using Transaction file (Roll, Code Add/Delete). Both files are sorted by Roll.

Metadata¶

Property	Detail
Author	Amit Dutta amitdutta4255@gmail.com
Date	08 Feb 2026
License	MIT License (See the LICENSE file for details)
Difficulty	Advanced (index: 6 / 10)

Concepts¶

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Array
Pointers
Iteration
Sorting (possible)
Recursion

Actions¶

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Source Code¶

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

struct student {
    int roll;
    char name[30];
};

struct trans {
    int roll;
    char code; // 'A' for Add, 'D' for Delete
    char name[30]; // Only needed for Add
};

void create_files();

int main()
{
    FILE *fm, *ft, *fn;
    struct student m;
    struct trans t;
    int has_m, has_t;

    create_files();

    fm = fopen("MASTER.DAT", "rb");
    ft = fopen("TRANS_ROLL.DAT", "rb");
    fn = fopen("NEW_MASTER.DAT", "wb");

    if (!fm || !ft || !fn) exit(1);

    has_m = fread(&m, sizeof(struct student), 1, fm);
    has_t = fread(&t, sizeof(struct trans), 1, ft);

    printf("Merging Master and Transaction files...\n");

    while (has_m && has_t)
    {
        if (m.roll < t.roll)
        {
            // No transaction for this master record, keep it
            fwrite(&m, sizeof(struct student), 1, fn);
            has_m = fread(&m, sizeof(struct student), 1, fm);
        }
        else if (m.roll == t.roll)
        {
            // Transaction affects this record
            if (t.code == 'D')
            {
                printf("Deleting Roll %d\n", m.roll);
                // Skip writing 'm' to file (Deleting)
                has_m = fread(&m, sizeof(struct student), 1, fm);
            }
            else
            {
                // Logic error: Can't ADD if ID exists. Maybe Update?
                // Assuming replace or skip. Let's skip T and keep M for now.
                has_m = fread(&m, sizeof(struct student), 1, fm);
            }
            has_t = fread(&t, sizeof(struct trans), 1, ft);
        }
        else // m.roll > t.roll
        {
            // Transaction ID is new
            if (t.code == 'A')
            {
                struct student new_s;
                new_s.roll = t.roll;
                strcpy(new_s.name, t.name);
                fwrite(&new_s, sizeof(struct student), 1, fn);
                printf("Adding Roll %d\n", new_s.roll);
            }
            has_t = fread(&t, sizeof(struct trans), 1, ft);
        }
    }

    // Process remaining Master
    while (has_m)
    {
        fwrite(&m, sizeof(struct student), 1, fn);
        has_m = fread(&m, sizeof(struct student), 1, fm);
    }

    // Process remaining Transactions (Only Adds)
    while (has_t)
    {
        if (t.code == 'A')
        {
            struct student new_s = {t.roll, ""};
            strcpy(new_s.name, t.name);
            fwrite(&new_s, sizeof(struct student), 1, fn);
            printf("Adding Roll %d\n", new_s.roll);
        }
        has_t = fread(&t, sizeof(struct trans), 1, ft);
    }

    fclose(fm); fclose(ft); fclose(fn);
    return 0;
}

void create_files()
{
    struct student m[] = {{10, "A"}, {20, "B"}, {30, "C"}};
    struct trans t[] = {{15, 'A', "NewGuy"}, {20, 'D', ""}, {40, 'A', "LastGuy"}};

    FILE *f1 = fopen("MASTER.DAT", "wb");
    fwrite(m, sizeof(struct student), 3, f1);
    fclose(f1);

    FILE *f2 = fopen("TRANS_ROLL.DAT", "wb");
    fwrite(t, sizeof(struct trans), 3, f2);
    fclose(f2);
}

Explanation¶

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    You are explaining a C programming code to a beginner.

    STRICT RULES:

    - Only use the given code. Do NOT assume anything not present.

    - Do NOT add extra examples.

    - Keep explanation clear and short.

    - If something is unclear, say "Not clear from code".

    - Follow the exact format below. Do NOT change headings.

    FORMAT:

    [START]

    ## What it does

    (Explain the overall purpose in 1-2 sentences)

    ## Step-by-step

    (Explain how the code works in steps, simple language)

    ## Key Concepts

    (List concepts like loop, condition, function, etc.)

    ## Notes

    (Mention any limitations, errors, or assumptions)

    [END]

    CODE (luc093.c):

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

    struct student {
        int roll;
        char name[30];
    };

    struct trans {
        int roll;
        char code; // 'A' for Add, 'D' for Delete
        char name[30]; // Only needed for Add
    };

    void create_files();

    int main()
    {
        FILE *fm, *ft, *fn;
        struct student m;
        struct trans t;
        int has_m, has_t;

        create_files();

        fm = fopen("MASTER.DAT", "rb");
        ft = fopen("TRANS_ROLL.DAT", "rb");
        fn = fopen("NEW_MASTER.DAT", "wb");

        if (!fm || !ft || !fn) exit(1);

        has_m = fread(&m, sizeof(struct student), 1, fm);
        has_t = fread(&t, sizeof(struct trans), 1, ft);

        printf("Merging Master and Transaction files...\n");

        while (has_m && has_t)
        {
            if (m.roll < t.roll)
            {
                // No transaction for this master record, keep it
                fwrite(&m, sizeof(struct student), 1, fn);
                has_m = fread(&m, sizeof(struct student), 1, fm);
            }
            else if (m.roll == t.roll)
            {
                // Transaction affects this record
                if (t.code == 'D')
                {
                    printf("Deleting Roll %d\n", m.roll);
                    // Skip writing 'm' to file (Deleting)
                    has_m = fread(&m, sizeof(struct student), 1, fm);
                }
                else
                {
                    // Logic error: Can't ADD if ID exists. Maybe Update?
                    // Assuming replace or skip. Let's skip T and keep M for now.
                    has_m = fread(&m, sizeof(struct student), 1, fm);
                }
                has_t = fread(&t, sizeof(struct trans), 1, ft);
            }
            else // m.roll > t.roll
            {
                // Transaction ID is new
                if (t.code == 'A')
                {
                    struct student new_s;

    ... (truncated for brevity)

luc093.c¶