'dos.h'

The headerfile "dos.h" is used to perform some system functions like :

* delay()
* sleep()
* getdate()
* gettime()
* setdate()
* settime()
* sound()
* nosound()

'delay()' and 'sleep()' :
 these are two similar functions used to make delay in the ouput of the program.

 for example :
 #include<iostream.h>
 #include<conio.h>
 #include<dos.h>
 int main()
{
    cout<<"This c++ program will exit in 10 seconds.\n";      

    delay(10000);                      

    return 0;
}

and same thing can be executed through 'sleep(10)'.

'gettime()' and 'getdate()':

these two functions are used to get the time and date of the system in the program.

for example
 #include<iostream.h>
#include<conio.h>
#include<dos.h>
#include<stdlib.h>
void main()
{
  clrscr();
  struct date d;
  struct time t;
  getdate(&d);
  gettime(&t);
  int day,month,year;
  int hour,min,sec;
  day=d.da_day;
  month=d.da_mon;
  year=d.da_year;
  hour=t.ti_hour;
  min =t.ti_min;
  sec= t.ti_sec;
  cout<<"The current date is "<<day<<"/"<<month<<"/"<<year<<"\n";
  cout<<"The current time is "<<hour<<":"<<min<<":"<<sec<<"\n";
  system("pause");
  }

output :

  The current date is 22/10/2015
  The current time is 11:24:05
  Press any key to continue.

'setdate()' and 'settime()' :
through these functions we can set the date and time of the system simply using the fuctions:
setdate(&var); and
settime(&var);
note:the members like 'd.da_day' should be integeral always.

'sound()' and 'unsound()':
functions used for adding sound.

example :

#include<dos.h>
void main()
{
for(i=100;i<=1000;i+20)
{
  sound(i);
  delay(50);
}
unsound();
system("pause");
}