1. Open num1.txt and read all integers into array a[]
2. Open num2.txt and read all integers into array b[]
3. Copy both arrays into a combined array c[]
4. Sort c[] using Bubble Sort (ascending order)
5. Open file3.txt for writing
6. Write every element of sorted c[] into file3.txt
7. Close all files

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

int main()
{
    FILE *f1, *f2, *f3;
    int a[100], b[100], c[200];
    int n1 = 0, n2 = 0;
    int i, j, k = 0, temp;

    /* ---- Step 1: Read integers from num1.txt ---- */
    f1 = fopen("num1.txt", "r");
    if (f1 == NULL)
    {
        printf("Error: Cannot open num1.txt\n");
        exit(1);
    }
    while (fscanf(f1, "%d", &a[n1]) != EOF)
    {
        n1++;
    }
    fclose(f1);

    /* ---- Step 2: Read integers from num2.txt ---- */
    f2 = fopen("num2.txt", "r");
    if (f2 == NULL)
    {
        printf("Error: Cannot open num2.txt\n");
        exit(1);
    }
    while (fscanf(f2, "%d", &b[n2]) != EOF)
    {
        n2++;
    }
    fclose(f2);

    /* ---- Step 3: Combine both arrays into c[] ---- */
    for (i = 0; i < n1; i++)
        c[k++] = a[i];

    for (i = 0; i < n2; i++)
        c[k++] = b[i];

    /* ---- Step 4: Sort c[] using Bubble Sort ---- */
    for (i = 0; i < k - 1; i++)
    {
        for (j = 0; j < k - i - 1; j++)
        {
            if (c[j] > c[j + 1])
            {
                /* Swap */
                temp    = c[j];
                c[j]    = c[j + 1];
                c[j + 1] = temp;
            }
        }
    }

    /* ---- Step 5: Write sorted integers to file3.txt ---- */
    f3 = fopen("file3.txt", "w");
    if (f3 == NULL)
    {
        printf("Error: Cannot open file3.txt\n");
        exit(1);
    }
    for (i = 0; i < k; i++)
    {
        fprintf(f3, "%d\n", c[i]);
    }
    fclose(f3);

    printf("Merged and sorted successfully into file3.txt\n");
    return 0;
}

        +----------+
        |  START   |
        +----------+
             |
             v
   +------------------+
   |  Read A, B, C    |
   +------------------+
             |
             v
       +------------+
       |   Is A > B? |
       +------------+
       /             \
     YES              NO
      |                |
      v                v
  +--------+       +--------+
  |Is A > C?|      |Is B > C?|
  +--------+       +--------+
  /        \       /        \
YES         NO   YES         NO
 |           |    |           |
 v           v    v           v
+---+      +---+ +---+      +---+
| A |      | C | | B |      | C |
|is |      |is | |is |      |is |
|Lar|      |Lar| |Lar|      |Lar|
|gest      |gest |gest      |gest
+---+      +---+ +---+      +---+
  \           \    /           /
   \           \  /           /
    \           \/           /
     \     +----------+     /
      \    |  Print   |    /
       +-->| Largest  |<--+
           +----------+
                |
                v
           +--------+
           |  STOP  |
           +--------+

START
  |
  Read A, B, C
  |
  Is A > B?
  ├── YES --> Is A > C?
  │           ├── YES --> Print "A is Largest"
  │           └── NO  --> Print "C is Largest"
  |
  └── NO  --> Is B > C?
              ├── YES --> Print "B is Largest"
              └── NO  --> Print "C is Largest"
  |
STOP