Question

When a hardware value might change due to external circumstances or a value might change due to an interrupt, what type modifier do you attach to the variable that might change?

C

Embedded Systems

Answer 1

Answer: Embedded Systems modifier can be used.

Explanation: As in Embedded Systems, there is a Volatile modifier in which the declaration is done outside a function block which can be use as a warning to the compiler that if there is any change in the event then the value assigned can be changed. The change in the hardware can also change the value.

For example:

We will be implementing two different codes, one by using "volatile" keyword and another without using it.

CODE No. 1:

#include<stdio.h>

int a = 1;

int main()

{

if (a == 1) //always true

  {

print{" a = 1 \n");

}

else        // a will never be other than 1
{
printf(" a != 1 \n");
}
   return 0;
}

In the above code, there is no any "volatile" keyword used. Therefore, the else part can be optimized as there is no use of the else part. The value of variable "a" can never change in the above code, therefore, there is no meaning in using the else part.

Let us see a code by using "volatile" keyword and try to optimize the code.

CODE No. 2:

#include<stdio.h>

volatile int a;    /* volatile Keyword*/

int main()
{
  
a = 2;
  
   if (a == 2)
   {
   printf(" a = 2 \n");
   }
   else       // possibility of change in the value of variable "a" due to volatile.   
   {  
   printf(" a != 2 \n");
   }
  
   return 0;
}

In the above code, "volatile" keyword is used. This makes the variable "a" changeable. when the value of "a" is 2, then the else part is not implemented but when the value of "a" changes, the else art comes in implementation. Therefore, if there will be a change due to external circumstances or due to an interrupt then the value of the variable can be changed.