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const int ledPin = 12;
void setup(){
 pinMode(ledPin, OUTPUT);
 Serial.begin(9600);
}
void loop(){
 if (Serial.available()) {
 light(Serial.read() – '0');
 }
 delay(500);
}
void light(int n){
 for (int i = 0; i < n; i++) {
 digitalWrite(ledPin, HIGH);
 delay(100);
 digitalWrite(ledPin, LOW);
 delay(100);
 }
}

by Oscar Liang

awesome little piece of code which taught me how to setup connection by serial. yet one part I don't understand fully. Why does this line:

light(Serial.read() – '0');

make the code run once, and this line an infinite times.

light(Serial.read());

has this something to do with binary? I don't get why subtracting the string 0 would run the code once.

Thanks in Advance!