How can I stop a loop with serial input - c++

Question

How can I stop or exit from this loop using a serial input?
This is the simple code I've been using
#define stimulation 4
#define led 13
void setup() {
Serial.begin(57600);
pinMode(stimulation,OUTPUT);
pinMode(led, OUTPUT);
digitalWrite(stimulation, LOW);
digitalWrite(led, LOW);
Serial.println("Press any Key");
while (!Serial.available()){}
}
void loop() {
digitalWrite(stimulation, HIGH);
digitalWrite(led, HIGH);
delay(20);
digitalWrite(stimulation, LOW);
digitalWrite(led, LOW);
delay(30);
}
I was looking for a serial input string to exit the loop
void loop() {
digitalWrite(stimulation, HIGH);
digitalWrite(led, HIGH);
delay(20);
digitalWrite(stimulation, LOW);
digitalWrite(led, LOW);
delay(30);
}
Thank you!

Answer 1

As your code will work without the serial monitor, you can try this snippet:
void setup() {
/* other codes */
Serial.begin(57600);
int numTries = 0;
while (!Serial.available()){
if( ++numTries >= 10) break;
delay(100);
}
}
Edited: I was assuming that you got stuck during the initial setup stage when Serial monitor don't respond. Since you like to blink the LED only once, you can do like so using static keyword. When a variable is declared as static, space for it gets allocated for the lifetime of the program.
void loop() {
static bool done = false; // will initialize only once
digitalWrite(stimulation, HIGH);
digitalWrite(led, HIGH);
delay(20);
digitalWrite(stimulation, LOW);
digitalWrite(led, LOW);
delay(30);
if(!done && Serial.available()) {
Serial.println("Stimulation Done :)");
done = true;
}
}

Answer 2

#define stimulation 4
#define led 13
unsigned long startMillis;
unsigned long currentMillis;
const unsigned long stimTime = 20*60000; // Stimulation Time (60s = 60000ms)
void setup() {
Serial.begin(115200);
pinMode(stimulation,OUTPUT);
pinMode(led, OUTPUT);
digitalWrite(stimulation, LOW); // force laser OFF before starting
digitalWrite(led, LOW);
Serial.println("Standby:");
Serial.println("Press any key to start stimulation");
while (!Serial.available()){} // do absolutely nothing until serial input received
startMillis = millis(); // time (ms) when input received
Serial.println("Now you wait 20min :)");
}
void loop() {
currentMillis = millis(); // time (ms) beginning of the loop
if (currentMillis - startMillis <= stimTime) {
digitalWrite(stimulation, HIGH); // Laser ON
digitalWrite(led, HIGH); // Internal Led ON
delay(20); // Keep laser ON for 20ms
digitalWrite(stimulation, LOW); // Laser OFF
digitalWrite(led, LOW); // Internal Led OFF
delay(30); // Keep laser OFF for 30ms
}
else { // After 20min do nothing (stop stimulation)
}
}