Sorting of dates using bubble sort

/* Sorting of dates using bubble sort. */

Take any five dates in dd\mm\yyyy format, and arrange them in asscending order.

Steps to develop the program:
1. Dates are entered as strings.
2. Convert the dates into integer values.
3. Check for validation of dates.
4. Sort the dates with respect to their integer values.
5. Display the sorted dates.

To increase the range of dates, we have stored it in 4 bytes using a long intger variable (Under DOS dates are stored in 2 bytes). So to store the day the lower 5 bytes are used. Now to store a month in next 4 bytes we need to multiply the month by 32. Similarly, to store the year it is multiplied by 512. This is done because we are required to store the entire date in one single entity, which is later used to sort the dates.

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

int d, m ;
long int y ;

void main( )
{
char dates[5][12], temp[12] ;
long int arr[5], t ;
int i, j, valid ;

int isvalid( ) ;
long int getnum ( char * ) ;

clrscr( ) ;

printf ( "Enter any five dates (dd\\mm\\yyyy) :-\n" ) ;
for ( i = 0 ; i <= 4 ; i++ )
{
printf("%d) ",i + 1 ) ;
scanf ( "%s", dates[i] ) ;

/* Converts date in string to equivalent integer values. */
arr[i] = getnum ( dates[i] ) ;

/* Checks for valid date. */
valid = isvalid( ) ;

if ( !valid )
{
printf ( "This date does not exists. " ) ;
printf ( "Enter any other date.\n" ) ;
i-- ;
}
}

/* Sorting of dates using Bubble sort method. */
for ( i = 0 ; i <= 3 ; i++ )
{
for ( j = 0 ; j <= 3 - i ; j++ )
{
if ( arr[j] > arr[j + 1] )
{
t = arr[j] ;
arr[j] = arr[j + 1] ;
arr[j + 1] = t ;

strcpy ( temp, dates[j] ) ;
strcpy ( dates[j], dates[j + 1]) ;
strcpy ( dates[j + 1], temp ) ;
}
}
}

printf ( "Dates in sorted order are :- \n" ) ;
for ( i = 0 ; i <= 4 ; i++ )
printf ( "%s\n", dates[i] ) ;

getch( ) ;
}

/* checks valid date */
int isvalid ( )
{
int isleap ( long int ) ;

if ( y <= 0 || m <= 0 || d <= 0 || m > 12 || y > 16384 ||
( m == 2 && !isleap ( y ) && d > 28 ) ||
( m == 2 && isleap ( y ) && d > 29 ) ||
( ( m == 1 || m == 3 || m == 5 || m == 7 || m == 8 || m == 10
|| m == 12 ) && d > 31 ) || ( ( m == 4 || m == 6 || m == 9 ||
m == 11 ) && d > 30 ) )
return 0 ;
else
return 1 ;
}

/* checks whether the given year is leap or not */
int isleap ( long int y )
{
return ( y % 4 == 0 ) ^ ( y % 100 == 0 ) ^ ( y % 400 == 0 ) ;
}

/* converts dates in string into equivalent integer values */
long int getnum ( char *date )
{
char *p, str[15] ;
long int num = 0 ;

strcpy ( str, date ) ;

d = m = y = 0 ;
p = strtok ( str, "\\" ) ;
if ( p != NULL )
d = num = atoi ( p ) ;

p = strtok(NULL, "\\");
if ( p != NULL )
m = atoi ( p ) ;
num += m * 32 ;

p = strtok(NULL, "\\");
if ( p != NULL )
y = atol ( p ) ;
num += y * 512L ;

return num ;
}