how do I cause a function of my code to stop running when another one runs.

Projects Programming
2

Below as a public service :wink: is the OP's code in code tags, with the white space tidied up a bit, and the { and } on their own lines, and control-T'd for formatting:

#include <Servo.h>
#include <Wire.h>
#include <LSM303.h>

LSM303 compass;
Servo myservo;
int DISTANCE = 0;
int servoPin = 3;       // Pin that the servomotor is connected to
int solenoidPin = 2;    // Pin that the mosfet is conected to
int switchPin = 4;      // Pin that the switch is conected to
int pos = 0;            // variable to store the servo position
int switchState;
int servoDir = 0;
int solenoidState = LOW;
unsigned long previousMillis = 0;        // will store last time LED was updated
const long interval = 1000;           // interval at which to blink (milliseconds)


void setup()
{
  myservo.attach(servoPin);               // attaches the servo on pin 9 to the servo object
  pinMode(solenoidPin, OUTPUT);           //Sets the pin as an output
  pinMode(switchPin, INPUT_PULLUP);       //Sets the pin as an input_pullup
  Serial.begin(9600);                     // starts serial communication @ 9600 bps
  Wire.begin();
  compass.init();
  compass.enableDefault();
}

void loop()
{

  ////////////// MAGNETOMETER ///////////////////////////////////////////////////
  compass.read();
  float heading = compass.heading();


  ////////////// SERVOMOTOR ///////////////////////////////////////////////////

  if (heading >= 230 && heading <= 250)
  {
    pos = 90;
  }

  if (heading > 250)
  {
    pos = 45;
  }

  if (heading < 230)
  {
    pos = 135;
  }

  myservo.write(pos);              // tell servo to go to position in variable 'pos'
  delay(10);


  ////////////// SOLENOID VALVE ///////////////////////////////////////////////////
  unsigned long currentMillis = millis();
  if (currentMillis - previousMillis >= interval)
  {
    previousMillis = currentMillis;
    if (solenoidState == LOW)
    {
      solenoidState = HIGH;
    }
    else
    {
      solenoidState = LOW;
    }
    digitalWrite(solenoidPin, solenoidState);    //Switch Solenoid ON/oFF
  }



  ////////////// REED SWITCH ///////////////////////////////////////////////////
  switchState = digitalRead(switchPin);

  if (switchState == 1)
  {
    DISTANCE = DISTANCE + 10;
  }


  ////////////// Distance  ///////////////////////////////////////////////////////
  ////////////// Serial Print  ///////////////////////////////////////////////////
  Serial.print("Reed Switch: ");
  Serial.print(switchState);
  Serial.print("   Magnetometer: ");
  Serial.println( heading );
  //Serial.print(" Distance");
  // Serial.println(DISTANCE);

  delay(100);
}