Voltage Measurement using Arduino

float input_volt = 0.0;
float temp=0.0;
float r1=10000.0;    //r1 value
float r2=100000.0;      //r2 value

void setup()
{
   Serial.begin(9600);     //  opens serial port, sets data rate to 9600 bps
}

void loop()
{
    int analogvalue = analogRead(A0);
    temp = (analogvalue * 5.0) / 1024.0;  // FORMULA USED TO CONVERT THE VOLTAGE
    input_volt = temp / (r2/(r1+r2));
    if (input_volt < 0.1) 
    {
      input_volt=0.0;
    } 
    Serial.print("Voltage= ");                 // prints the voltage value in the serial monitor
    Serial.print(input_volt);
    Serial.println(" Volts");
    delay(1000);
}