Trouble with array

[magsto]

Hello!

I'm having some frustrating errors with the Arduino that I can't understand, I'm using a function to build an array. It takes a value, divides it into a given number of equal parts, and puts these parts in the array. My program is supposed to make 20, so I make an array with a set size of 20. Trouble is when I print it directly after making it, the size is 40. The first 20 values in the array are correct, but the other 20 are complete nonsense that I don't understand. Leaving the code below for reference.

int myArray[20];

void buildArray(int totalLength) {
. int piece = totalLength / sizeof(myArray);
. for (int e = 0; e < sizeof(myArray); e++) {
. . myArray[e] = (e + 1) * piece;
. }
}

(Sorry for the ugly code I couldn't find out how to add it here)

Now when I print the size of the array, followed by iterating through this and printing each value in the array I get the following nonsense:

40

440
880
1320
1760
2200
2640
3080
3520
3960
4400
4840
5280
5720
6160
6600
7040
7480
7920
8360
8800
0
0
0
2200
4400
6600
8800
0
9216
1
-6144
3
0
0
-15104
-15360
-16384
-16128
-15872
-14848

Hope someone is able to help, as it is driving me mad, and is a part of an assignment to be delivered very soon.

Thank you

[Whandall]

sizeof() returns the number of bytes used, not the number of elements.

You can divide that value by the size of a single element to get the number of elements.

[UKHeliBob]

 sizeof(myArray)

This will return the number of bytes used by the array, not the number of elements in the array. You are using an array of ints, each of which take 2 bytes. Do you see the problem ?

Using this instead

 sizeof(myArray) / sizeof(myArray[0])

will give the number of elements for an array of any kind

[magsto]

That makes sense! Now, for some reason, when I iterate through it says the size of the array is 2. My code looks like this:

Serial.println(sizeof(myArray[0]);
for (int e = 0; e < sizeof(myArray[0]); e++) {
. Serial.println(myArray[e]);
}

Gives the following output

2
440
880

[UKHeliBob]

sizeof(myArray[0])
Yes, that will be 2

Read my previous reply more carefully

[magsto]

Ah man sorry my bad haha, makes perfect sense now, thank you very much! Reckon I can get it working now. So these extra numbers they just showed up randomly? In other languages this would throw an index error in this instant right?

[UKHeliBob]

The other numbers were whatever was in the memory locations when you read them. Luckily you did not write to then because that may have corrupted other variables