How to store values from a sensor inside an empty array?

Question

I need to store the value of the distance in the dist array, then calculate the maximun value and print the index associated with this value:

The problem is when starting the nested for inside another for, the servomotor stops working

// Includes the Servo library
#include <Servo.h>
// Array y valores para funcion valor maximo
int max=0;
int angle=0;
int distance=0;
// Defines Tirg and Echo pins of the Ultrasonic Sensor
const int trigPin = 10;
const int echoPin = 11;
// Variables for the duration and the distance
long duration;
//int distance[180];
Servo myServo1; // Creates a servo object for controlling the servo motor
void setup() {
 pinMode(trigPin, OUTPUT); // Sets the trigPin as an Output
 pinMode(echoPin, INPUT); // Sets the echoPin as an Input
 Serial.begin(9600);
 myServo1.attach(12); // Defines on which pin is the servo motor attached
 }
void loop() {
distance = calculateDistance();
 if (distance <= 15 && distance >=2)
 {
 // rotates the servo motor from 1 to 179 degrees and calculate the distance at each angle
 for(int j=90;j>=0;j--){
 myServo1.write(j);
 delay(30);}
 for(int j=0;j<=180;j++){ 
 myServo1.write(j); 
 int i=0; 
 int dist [i] = {calculateDistance()};
 for (i=0;i=180;i++){ <--------------------------------------
 if (dist[i]>max){
 max=dist[i];
 angle=i;
 Serial.print(angle);
 delay(30);}
 }
 }
 // Repeats the previous lines from 179 to 90 degrees
for(int j=180;j>90;j--){ 
 myServo1.write(j);
 delay(30);
 }
}
}
// Function for calculating the distance measured by the Ultrasonic sensor
int calculateDistance(){ 
 digitalWrite(trigPin, LOW); 
 delayMicroseconds(2);
 // Sets the trigPin on HIGH state for 10 micro seconds
 digitalWrite(trigPin, HIGH); 
 delayMicroseconds(10);
 digitalWrite(trigPin, LOW);
 duration = pulseIn(echoPin, HIGH); // Reads the echoPin, returns the sound wave travel time in microseconds
 distance= duration*0.034/2;
 return distance;
}

Answer 1

 int i=0; 
 int dist [i] = {
 calculateDistance() };

I'm not sure what you are thinking here, but you obviously cannot store data into a zero-length array. You also cannot put a function call to populate an array of variable length.

You need to decide how many elements you need in the array, in advance, and allocate an array of that size.

---

Maybe more like this:

 int dist [180];
 for (i=0;i<180;i++){ 
 dist [i] = calculateDistance ();
 if (dist[i]>max){
 max=dist[i];
 angle=i;
 Serial.print(angle);
 delay(30);
 }
 }

---

Also, this is wrong in your code:

for (i=0;i=180;i++){ 

You need to test for < 180 here. Your for loop will assign 180 to i and then check to see if it is non-zero, which will always be true.

• StephanyCh: I modified this part of the code and the problem is the same. Actually I do not know if I'm saving the data in the array with this instruction :/
• StephanyCh: It doesn't do the first for loop instruction, the servo only runs from 0 to 90 degrees and stops working.
• Nick Gammon: You need to put in some debugging "prints". It's hard to tell what is happening. What value gets stored in distance, for example?
• StephanyCh: In distance variable gets stored the value of distance which was measured of the Ultrasonic Sensor.
• Nick Gammon: Obviously. I meant what number are you seeing? Zero? 20? 100?