Improve arduino for loop and void loop - arduino

Question

I have wrote code for my Arduino project. It has a for loop. After for loop done there is a void loop.
I am expecting starting gap should reduce from 100 to 0 and remains constant. But when the code runs it goes 100 to 0 and reset the values again to 100. Then again values will go to 100 to 0. This time it remains 0.
My issue is why it takes two time to remain 0.What are the changes I should do to code to get expected output.
Expected output is only one loop. 100 is reducing to 0. then remain 0.
thank you.
Expected output is like this. Sine wave is come from a AC supply. Please neglect the shape of sine and assume it as a pulse (PWM).
Code:
int minGap = 0;//motor full speed gap
int pulseWidth = 10;//pulse lenght
int startGap = 100;//starting gap
int gapReduseRate = 1;//gap reduse rate
void setup() {
// initialize digital pin LED_BUILTIN as an output.
pinMode(3, OUTPUT);
pinMode(9, OUTPUT);
pinMode(5, OUTPUT);
pinMode(6, OUTPUT);
for(int i=startGap ; i>minGap ; i=i-gapReduseRate){
digitalWrite(3, HIGH); // turn the LED on (HIGH is the voltage level)
digitalWrite(9, HIGH);
digitalWrite(5, HIGH);
digitalWrite(6, HIGH);// turn the LED on (HIGH is the voltage level)
delayMicroseconds(pulseWidth); // wait for a second
digitalWrite(3, LOW); // turn the LED off by making the voltage LOW
digitalWrite(9, LOW);
digitalWrite(5, LOW);
digitalWrite(6, LOW);// turn the LED off by making the voltage LOW
delayMicroseconds(i); // wait for a second
}
}
// the loop function runs over and over again forever
void loop() {
digitalWrite(3, HIGH); // turn the LED on (HIGH is the voltage level)
digitalWrite(9, HIGH);
digitalWrite(5, HIGH);
digitalWrite(6, HIGH);// turn the LED on (HIGH is the voltage level)
delayMicroseconds(pulseWidth); // wait for a second
digitalWrite(3, LOW); // turn the LED off by making the voltage LOW
digitalWrite(9, LOW);
digitalWrite(5, LOW);
digitalWrite(6, LOW);// turn the LED off by making the voltage LOW
delayMicroseconds(minGap); // wait for a second
}