class DATA{
public:
DATA(int A);
void Sensor();
}

DATA::DATA(int A){
MPU6050 mpu(A);
}

void Sensor(){
mpu.setFullScaleAccelRange(3);
// the problem is here, "mpu" object is not declared for this friend function
}

int main(){
DATA mpu1(0x68)
/* I'm using two MPU6050 on I2C bus so I need to address them.
 this example contains only one MPU6050 object*/
    return 0;
}