C program that is passed a virtual address on the command line and have it output the page number and offset for the given address

Assume that a system has a 32-bit virtual address with a 4-KB page size.
Write a C program that is passed a virtual address (in decimal) on the
command line and have it output the page number and offset for the
given address. As an example, your program would run as follows:
./a.out 19986
Your program would output:
The address 19986 contains:
page number = 4
offset = 3602
Writing this program will require using the appropriate data type to
store 32 bits.We encourage you to use unsigned data types as well.

Answer:

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/**
 * Program that masks page number and offset from an
 * unsigned 32-bit address.
 * The size of a page is 4 KB (12 bits)
 *
 * A memory reference appears as:
 *
 * |------------|-----|
 *  31      12 11  0
 *
 */
 
#include <stdio.h>
#include <unistd.h>
 
#define PAGE_NUMBER_MASK 0xFFFFF000
#define OFFSET_MASK 0x00000FFF
 
int main(int argc, char *argv[]) {
    if (argc != 2) {
        fprintf(stderr,"Usage: ./a.out <virtual address>\n");
        return -1;
    }
 
    int page_num, offset;
    unsigned int reference;
 
    reference = (unsigned int)atoi(argv[1]);
    printf("The address %d contains:\n",reference);
 
    // first mask the page number 
    page_num = (reference & PAGE_NUMBER_MASK) >> 12;
    offset = reference & OFFSET_MASK;
    printf("page number = %d\n",page_num);
    printf("offset = %d\n",offset);
 
    return 0;
}