Why do I need storing variable for printing value from analog read

Hi guys.
I just learned how to use analogRead command in arduino and have a problem.

I connected Arduino Uno with trimpot and wanted to read the voltage using analogRead command.
So, I connected the viper with the pin A3 and other legs of trimpot to the 5 V and GND.
In the tutorial, storing variable is used. For example:

int readvalpin=A3;
int readval;
float V2;

void setup() {
Serial.begin (9600);}

void loop () {
readval=analogRead (readvalpin);

Notice that I have used 2 different variables: readvalpin and readval. I used readvalpin variable to assign the analog pin that is connected to the wiper of potentiometer. Readval variable is used to store the value from the analog pin before print it to the serial monitor. If I use 2 variables, than I an read the voltage.
But, when I just use 1 variable, without storing variable, I read value 0,08.
Why this happened?

It's impossible to say unless you post the code that does that.

const byte readvalpin=A3;

void setup() 
  Serial.begin (9600);

void loop () 
  int readval=analogRead (readvalpin);
  float V2=readval/1024.0 * 5.0;

I think what you’re saying is “17 / 1023 * 5 is 0.08” ?


Hint: print the value of A3.

Using only one variable.

void loop () {
Serial.println(analogRead(readvalpin) / 1023.0 * 5.0);