How to int same item in different condition

int message2 = HIGH;
int message2 = LOW;

Example i want make message2 become HIGH and LOW because i want set a condition as

if (message2 = HIGH){

First, in your test, you need == instead of =

if (message2 == HIGH){

Your variable message2 should be changed somewhere in your code. LOW is an alias for 0. HIGH is everything else, so 1 is HIGH. Then if you want to switch between LOW and HIGH, you can do it as:

message2 = 1 - message2;

When you put a type in front of a variable name you are declaring a new variable with that data type and name. Only one variable of that name can exist in the same scope so it cannot be both HIGH and LOW at the same time.

To keep things simple declare the variable outside of a function at the start of the program. It will then be globally available throughout the program

When you want to set it to a value do not precede the variable name with a data type otherwise you will be declaring a new variable with the same name but different scope.

Incidentally, = is used to assign a value to a variable and == to test for equality between a variable and a value