How can we interpret the following program and its success?(Its obvious that there must not be any error message). I mean how does compiler interpret lines 2 and 3 inside main?
#include <stdio.h>
int main()
{
int a,b;
a; //(2)
b; //(3)
return 0;
}
Your
a;
is just an expression statement. As always in C, the full expression in expression statement is evaluated and its result is immediately discarded.
For example, this
a = 2 + 3;
is an expression statement containing full expression a = 2 + 3. That expression evaluates to 5 and also has a side-effect of writing 5 into a. The result is evaluated and discarded.
Expression statement
a;
is treated in the same way, except that is has no side-effects. Since you forgot to initialize your variables, evaluation of the above expression can formally lead to undefined behavior.
Obviously, practical compilers will simply skip such expression statements entirely, since they have no observable behavior.