How there is Lvalue required error

Question

There is a piece of code which is producing error of "Lvalue required". The code is as,

     #include<stdio.h>
     #include<conio.h>
     #define max 10
     int main()
     {
      printf("%d",max++);
      return 0;
     }

It was evident that Lvalue error will come in above code so i changed the code to

     int a;
     printf("%d",a=max++); 

I thought now the value of constant is assigned to a proper variable but still the error appeared. Then i checked for

     printf("%d",a=max+1);

it works without any error.What is the problem with the second piece of code ?

Answer 1

max is a literal so max++ will fail. (Just as 10++ will fail).

However, max + 1 is valid (just as 10 + 1 is).

Remember that #defines are resolved by the preprocessor which happens before compilation takes place.

To explain your compiler's return error:

Loosely speaking, an lValue is the thing on the left hand side of an assignment; i.e. in

a = b;

a is the lValue. The statement 10 = b; is clearly meaningless (you can't assign a value to 10): more formally it is invalid since 10 is not an lValue.

Answer 2

max will be replaced by 10 after preprocessing, so

max++ => 10++      //Error  ++ requires lvalue
a=max++ => a=10++  //Error  same as above

a=max+1 => a=10+1 //Works