error for variable question

Question

It says variables must be declated before their use. They can actually be used at the time of their decleration (for loop for example)

Answer 1

in a loop you do have to declare a variable before or while using it. example
here we declare a local variable used in the for loop
for (int x=0; x<5; x++) printf("x=%d",x);

Answer 2

it means if it never existed in the first place

Answer 3

as in int a vs just using a without the int

Answer 4

The first parameter in a for loop is the decleration. You can not point to something that does not exist.