C program to convert Big Endian to Little Endian - Endianness

We need to know few things before knowing about Endianness.

What is a word?
1 word = 4 bytes.

What is a byte?
1 byte = 8 bits.

How the data are stored in memory?
Consider an integer num and it holds the value 12345.  Size of an integer is 4 bytes.  "num" is an integer and its size should be 4 bytes.  The hexadecimal value of 12345 is 0x3039.

Writing 0x3039 in word format(Big Endian).
+-------------------------+
| 00 |  00  |  30  |  39 |
+-------------------------+

Writing 0x3039 in word format(Little Endian).
+-------------------------+
| 39 |  30  |  00  |  00 |
+-------------------------+

The data would be stored in the above format in memory.

Big Endian stores the Most significant byte at the smallest address.

  Address        Value
+------------------------------------+
| 0x45325  |     00                   |
+------------------------------------+
| 0x45326  |     00                   |
+------------------------------------+
| 0x45327  |     30                   |
+------------------------------------+
| 0x45328  |     39                   |
+------------------------------------+

Little Endian stores the Least Significant byte at the smallest address
  Address        Value
+------------------------------------+
| 0x45325  |     39                   |
+------------------------------------+
| 0x45326  |     30                   |
+------------------------------------+
| 0x45327  |     00                   |
+------------------------------------+
| 0x45328  |     00                   |
+------------------------------------+

Write a C program to convert Big Endian to Little Endian.

  #include <stdio.h>
  int main () {
        int num, i, val;
        char *ptr;

        /* get the integer input from user */
        printf("Enter your input:");
        scanf("%d", &num);
        ptr = (char *)(&num);

        printf("Hexadecimal value of %d is 0x%x\n", num, num);

        /* Writing byte by byte to get big endian format */
        printf("Big Indian Format   : ");
        for (i = 0; i < sizeof(int); i++) {
                val = *(ptr + i);
                printf("|0x%x", val);
        }
        printf("|\n");

        /* writing byte by byte to get little endian format */
        printf("Little Indian Format: ");
        for (i = sizeof(int) - 1; i >= 0; i--) {
                val = *(ptr + i);
                printf("|0x%x", val);
        }
        printf("|\n");
        return 0;
  }

  Output:

  jp@jp-VirtualBox:~/$ ./a.out
  Enter your input:12345
  Hexadecimal value of 12345 is 0x3039
  Big Indian Format   : |0x0|0x0|0x30|0x39|
  Little Indian Format: |0x39|0x30|0x0|0x0|