Tail command implementation

// C++ program to implement your own tail
#include <bits/stdc++.h>
using namespace std;

#define SIZE 100

// Utility function to sleep for n seconds
void sleep(unsigned int n)
{
	clock_t goal = n * 1000 + clock();
	while (goal > clock());
}

// function to read last n lines from the file
// at any point without reading the entire file
void tail(FILE* in, int n)
{
	int count = 0; // To count '\n' characters

	// unsigned long long pos (stores upto 2^64 – 1
	// chars) assuming that long long int takes 8
	// bytes
	unsigned long long pos;
	char str[2*SIZE];

	// Go to End of file
	if (fseek(in, 0, SEEK_END))
		perror("fseek() failed");
	else
	{
		// pos will contain no. of chars in
		// input file.
		pos = ftell(in);

		// search for '\n' characters
		while (pos)
		{
			// Move 'pos' away from end of file.
			if (!fseek(in, --pos, SEEK_SET))
			{
				if (fgetc(in) == '\n')

					// stop reading when n newlines
					// is found
					if (count++ == n)
						break;
			}
			else
				perror("fseek() failed");
		}

		// print last n lines
		printf("Printing last %d lines -\n", n);
		while (fgets(str, sizeof(str), in))
			printf("%s", str);
	}
	printf("\n\n");
}

// Creates a file and prints and calls tail() for
// 10 different values of n (from 1 to 10)
int main()
{
	FILE* fp;
	char buffer[SIZE];
	// Open file in binary mode
	// wb+ mode for reading and writing simultaneously
	fp = fopen("input.txt", "wb+");
	if (fp == NULL)
	{
		printf("Error while opening file");
		exit(EXIT_FAILURE);
	}
	srand(time(NULL));

	// Dynamically add lines to input file
	// and call tail() each time
	for (int index = 1; index <= 10; index++)
	{
		/* generate random logs to print in input file*/
		for (int i = 0; i < SIZE - 1; i++)
			buffer[i] = rand() % 26 + 65; // A-Z
		buffer[SIZE] = '\0';

		/* code to print timestamp in logs */
		// get current calendar time
		time_t ltime = time(NULL);

		// asctime() returns a pointer to a string
		// which represents the day and time
		char* date = asctime(localtime(<time>));

		// replace the '\n' character in the date string
		// with '\0' to print on the same line.
		date[strlen(date)-1] = '\0';

		/* Note in text mode '\n' appends two characters,
		so we have opened file in binary mode */
		fprintf(fp, "\nLine #%d [%s] - %s", index,
									date, buffer);

		// flush the input stream before calling tail
		fflush(fp);

		// read last index lines from the file
		tail(fp, index);

		// sleep for 3 seconds
		// note difference in timestamps in logs
		sleep(3);
	}

	/* close the file before ending program */
	fclose(fp);

	return 0;
}