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https://wokwi.com/projects/347478624767574611

Using 3 utrasound sensors without libraries and one LED

const byte numSensors = 3; //const means constant variables, byte means small space in memory, numSensors is the variable name.
const byte ECHO_PIN[numSensors] = {2, 5, 8}; //we create an array to be used in a for loop
const byte TRIG_PIN[numSensors] = {3, 4, 7};

void setup() {
  Serial.begin(115200);
  pinMode(LED_BUILTIN, OUTPUT);
  for (byte s=0; s< numSensors; s++) { /* due to for loop, we reduce pinMode instructions from 6 to only 2:
                                        pinMode(3, OUTPUT);
                                        pinMode(2, INPUT); 
                                        pinMode(4, OUTPUT);
                                        pinMode(5, INPUT); 
                                        pinMode(7, OUTPUT);
                                        pinMode(8, INPUT); */
    pinMode(TRIG_PIN[s], OUTPUT);
    pinMode(ECHO_PIN[s], INPUT);
  }
}

float readDistanceCM(byte s) { 
/* This is a function with a parameter (s) and return a value that depends on the duration of a pulseIn function and a mathematical
calculus with the velocity of sound*/
  digitalWrite(TRIG_PIN[s], LOW); 
  /*We need to have the trigger pin controlled to a low value in order to measure the duration of the high value that is
  proportional to the distance of the sensor*/
  delayMicroseconds(2);
  digitalWrite(TRIG_PIN[s], HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG_PIN[s], LOW);
  int duration = pulseIn(ECHO_PIN[s], HIGH);
  return duration * 0.034 / 2; //divided by 2 because the ultrasound goes and returns back
}

void loop() {
  bool isNearby = false;
  Serial.print("Measured distance: ");
  for (byte s=0; s< numSensors; s++) {
    float distance = readDistanceCM(s);
    isNearby |= distance < 100;
    Serial.print(distance);
    Serial.print(" ");
  }
  Serial.println();
  digitalWrite(LED_BUILTIN, isNearby);
  delay(100);
}