the output pins are not effected by serial reading

Projects Programming
3

Please note that angle is a char so if you type 30 angle will be first 3 and thereafter it will be zero.

you must read in multiple characters, convert that into an integer and then you can do the motor math.

void loop()
{
 while (Serial.available()) 
  {
   char angle = Serial.read();
      
      Serial.println(angle);  // <<<<<<<<<<<<<<<<<<<<<< CHANGE THIS LINE TO SEE
      
  if(angle >= 0 && angle <= 30)
   
   {
    // write output for 'M1'
    analogWrite(pwm_motor1, LOW);
    digitalWrite(dir1,LOW);
    // write output for 'M2'
    analogWrite(pwm_motor2, LOW);
    digitalWrite(dir2,LOW);
   }
else if(angle > 30 && angle <= 90)
{
  analogWrite(pwm_motor1, HIGH);
    digitalWrite(dir1,LOW);
    // write output for 'M2'
    analogWrite(pwm_motor2, HIGH);
    digitalWrite(dir2,LOW);
   }
}
}

PS,
using CTRL-T in your IDE before posting, saving or uploading makes your code more readable!