#define VAR_1(a,b) a##b
#define VAR_2(a,b) VAR_1(a,b)
#define VAR(a) VAR_2(a,__COUNTER__)

int VAR(x) = 100;
int VAR(x) = 101;
int VAR(x) = 102;
int VAR(x) = 103;

void setup() 
{
  Serial.begin(115200);
  Serial.println(x0);
  Serial.println(x1);
  Serial.println(x2);
  Serial.println(x3);
}

void loop() 
{
  delay(10);
}