First question: A for loop executes the statement immediately following it, always. When you put multiple statements in braces *, they are executed as one statement. In other words you can either follow a for loop with a single statement, or with a code block.

Second Question: You can use multliple variables in a for loop like so:

1. for(int i = 0, j = 2; i < 10 && j < 21; i ++, j += 2) {
2.   println("i: " + i + ", " +  "j: " + j);
3. }

* I normally refer to the "{", "}" characters as braces to avoid confusion with brackets "[", "]".

Got ya. That totally makes sense. Multiple variables in for loop most handy as well. Thanks!

what about putting a variable instead of a number in your for loop? like this:

for (int i = fL; i < topLeftVid.length; i++)

the reason i want to do this is because i need a specific number which is randomly chosen earlier in the sketch

Yes, you can do this (and you could have tried...).

im' confused because i try a so much basic example and i don't understand how solve it.
Basically, i just want to create an int array of 0 or 1 and in a second array put the index of the first array > to 0.

like : int[] test{0,0,0,1,1,0,1}; int[] test2= new int[numbersofvalues]
  // 3 values of one in test[] and i get their index herein test2 so in this example it will be test2 = { 3,4,6 };

i use a basic method and i try with differents methods like splice() or arayCopy() but in fact the problem stay the same : i need to get differents values of i in a for loop to put my values indexed in my second array.

i think i miss something evident for my part and i your help could be an elegant hint to solve my problem


/////

int length = 10;
int index=0;
int[] test = new int[length];

int numbervaluesindexed = 0;



void setup() {

  for (int i = 0;  i < length ; i++) {
    test[i] = int(random(2));
    if (test[i]>0) {
      numbervaluesindexed ++
        ;
    }
  }
}

void draw() {


  int[] test2 = new int[numbervaluesindexed];
//I need to put this array indraw because i don't know in advance his lenght

  for (int i = 0;  i < length ; i++) {
    for (int j = 0;  j < numbervaluesindexed  ; j++) {
      if (test[i]>0) {
        index = i; 
        // this is the problem : index stay egual at the last value indexed
        test2[j] = index;
      }
    }
  }

  println(numbervaluesindexed );
  println(test2);
}

You don't need two nested loops, you only need to iterate over test[], and to maintain an index in test2[].

1. void draw() {
2.   noLoop();
   
3.   int[] test2 = new int[numbervaluesindexed];
4.   //I need to put this array indraw because i don't know in advance his lenght
5.   ^^^ you can declare it at the global level, and initialize it in draw()
   
6. 
   
7.   int j = 0;
8.   for (int i = 0;  i < length ; i++) {
9.     if (test[i]>0) {
10.       test2[j++] = i; // No need for index
    
11.     }
12.   }
13.   println(numbervaluesindexed );
14.   println(test2);
15. }