Triac control software

char c;
unsigned long current_time;
unsigned long start_time = 0;
unsigned long burst_start;
int triac = 13;
int cycle_legnth = 1000; //the legnth of each burst cycle
int burst_legnth; //the time that the triac is switched on

void setup() {
 pinMode(triac, OUTPUT);
 Serial.begin(115200);
}
void loop() {
 current_time = millis();
//Reading input from keyboard 0-9
if (Serial.available())
{
  c = Serial.read();
}
int n = c - '0';

burst_legnth = (((n)*(cycle_legnth))/10);

//Timing functions
if ((current_time) >= (start_time + cycle_legnth)) {
start_time = current_time;
burst_start = current_time;
Serial.println (n);
Serial.print("Triac on at ");
Serial.println (current_time);
digitalWrite(triac,HIGH);
}
else if ((current_time) >= (burst_start + burst_legnth)) {
digitalWrite(triac,LOW);
Serial.println(burst_legnth);
Serial.print("Triac off at ");
Serial.println (current_time);
  }
}