Arduino with labview

Hey, I am new on this forum, and new to the arduino platform, I want to control speed dc motor with L298 and arduino uno rev3. Problem isi dont know how to read a value between 0 and 255(8 bit value) from serial monitor(i task it), and after arduino read this value . need to set the duty cycle on analog write. Basicly the value that i task on serial is the duty cycle of PWM. I have a some kind of code but is does’nt work. Somebody more expert?

int M1 = 11;

int M2 = 12;

void setup() {
Serial.begin(9600); // opens serial port, sets data rate to 9600 bps
pinMode(M1, OUTPUT);

pinMode(M2, OUTPUT);

Serial.begin(9600);

}
void loop() {
if (Serial.available())
{
char ch = Serial.read();
if (ch >= ‘0’ && ch <= ‘256’)
{

analogWrite(M1,128);
analogWrite(M2,LOW);

}}

}

Servo test code that uses int n = readString.toInt(); to convert a neumeric character String into a number.

// zoomkat 10-22-11 serial servo test
// type servo position 0 to 180 in serial monitor
// or for writeMicroseconds, use a value like 1500
// for IDE 0022 and later
// Powering a servo from the arduino usually *DOES NOT WORK*.

String readString;
#include <Servo.h> 
Servo myservo;  // create servo object to control a servo 

void setup() {
  Serial.begin(9600);
  myservo.writeMicroseconds(1500); //set initial servo position if desired
  myservo.attach(7, 500, 2500);  //the pin for the servo control, and range if desired
  Serial.println("servo-test-22-dual-input"); // so I can keep track of what is loaded
}

void loop() {
  while (Serial.available()) {
    char c = Serial.read();  //gets one byte from serial buffer
    readString += c; //makes the string readString
    delay(2);  //slow looping to allow buffer to fill with next character
  }

  if (readString.length() >0) {
    Serial.println(readString);  //so you can see the captured string 
    int n = readString.toInt();  //convert readString into a number

    // auto select appropriate value, copied from someone elses code.
    if(n >= 500)
    {
      Serial.print("writing Microseconds: ");
      Serial.println(n);
      myservo.writeMicroseconds(n);
    }
    else
    {   
      Serial.print("writing Angle: ");
      Serial.println(n);
      myservo.write(n);
    }

    readString=""; //empty for next input
  } 
}

@zoomkat,
I’ve seen this code more often!

There is a potential bug in that reading the digits can be broken in 2 or more parts e.g. if time between digits is longer than the delay used.
It would be better to wait for a non-digit before parsing the int

while (Serial.available())
{
  char c = Serial.read();
  if ('0'<=c && c <= '9') readString += c;
  else break;
  delay(2);
}

There is a potential bug in that reading the digits can be broken in 2 or more parts e.g. if time between digits is longer than the delay used.It would be better to wait for a non-digit before parsing the int

That would assume a non digit is sent, such as a delimiter, along with the data. There is no appreciable delay in sending characters as a string from the serial monitor, so the delay in the code accommodates this. The code is just intended to be a very simple example using the serial monitor without changing the settings of the serial monitor, or sending anything beyond just the data desired.