Dear Harshada,

volatile is a keyword, it tells compiler that this variable may change its value due to something not known to compiler.

e.g. considor following segment

unsigned char ch;

unsigned char my_func(void)
{

ch = 0xFF;

....... //some code lines
....... //these lines donot change value of ch directly or indirectly
.......
.......

if(ch == 0)
{
return(0);
}
else
{
return(1);
}

}//end of my_func



in the above segment ch is global variable initialised to 0xFF.
hence while compiling if..else compiler knows value of ch is 0xFF, hence it will omit the if..else statement & returns 1 irrespective of value of ch.
it is possible that some ISR is making ch = 0, which compiler may fail to visualise.


On the other hand if we declare it as volatile compiler will compile if..else though it knows that ch is initialised to 0xFF.

Regards,
Mahesh