lvalue & rvalue

tushar_pandey · 08-21-2012, 11:33 PM

why and when we face these types of errors !

NevemTeve · 08-21-2012, 11:41 PM

They aren't errors. Quote the exact error message you got from the compiler.

piyush.sharma · 08-22-2012, 12:16 AM

Quote:

Originally Posted by tushar_pandey

why and when we face these types of errors !

"lvalue is required", this message is shown when you don't have a variable on the lift side of assignment. means we have a value but don;t have a space to store it.
try ++x++, it will display because after post increment, pre will be applied on incremented value of x. that will cause your message.

kedarp · 08-23-2012, 02:50 AM

You will encounter these when you especially work with pointers.
For e.g.

Code:

main()
{
   int a[10];
   
   //now if I try to change the address of the array a
   a++;
   
   //I will get that lvalue required because you are changing the base address of the array.
}

Or you could do this -

Code:

main()
{
   int a[10];
   int *b;
   b=a;         //assign the address of a to b;
   for(int i=0;i<a;i++)
      printf("%d ",*b++);    //and use b to access elements
}

sundialsvcs · 08-23-2012, 08:46 AM

It's a computer-science jargon: an lvalue is something that can legitimately appear on the left side of an assignment statement; rvalue on the right.

kedarp · 08-23-2012, 09:00 AM

In my previous post, a++ actually is a=a+1.
lvalue required is that you cannot assign a new value to a on LHS.
You have to take another variable, i.e. a pointer to 'a'

Code:

int *b;
b=a;
//a=a+1      //lvalue required
b++;         //will work