Reading Ints over Serial Monitor

read_serial.ino

int MOTORPIN = 9;
int analog_input = 82;
String input;

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

void loop() {
  Serial.print("Current Analog Value:");
  Serial.print(analog_input);
  Serial.print("\n");
  analogWrite(MOTORPIN, analog_input);
  Serial.println("Enter a number...");
  while(Serial.available() == 0){ } // wait for input
  while(Serial.available()) {
    // Read in a single character to the variable input
    char ch = Serial.read();
    input += ch;  
    delay(10); // Slow down loop a bit
  }

  int temp = input.toInt();
  if(temp > 255 || temp == 0){
    Serial.println("Invalid number entered!");
  } else {
    analog_input = temp;
  }

  input = "";
}