For Loop Question, syntax questions and fix needed

[Dana1954]

I received help on another topic and this included the for loop in the first function below. I tried using the same technique for unsigned long in the second function below.

The comments in the code are mine, just trying to understand what is going on. Also I'm a hardware guy, no formal programming education.

The below print function prints three values not 2. This seems to imply this code syntax is meant for character arrays and is expected a null character at the end? Will this for loop style work with long type as well as char types?

How can this be fixed.

// this is the code example followed to try coding the print() function below

void copyArrayAtoO(char a[], char out[]) {
	char *q;		// char input arrays pointer
	char *p = out;	// assign output array pointer
	
	// assign char a[] to q, *q ptr for char a[], inc char a[] ptr, inc out ptr
	for (q = a; *q; q++, p++)
		*p = *q; 
	
	*p = '\0'; // append null character
}

// code that needs help

unsigned long A[] = { 655390, 1310780 };

// call like this
print(A);

void print( unsigned long A[] )  {
	unsigned long *a; // pointer 
	
	for (a = A; *a; a++)  {
		Serial.println(*a);
	}		
}

[anon73444976]

You're relying on a char string being automatically terminated with a zero byte.
There is no such termination for other arrays.

To fix this, you need to pass the size of the array to the function.

@Dana1954

for (c = A; *a; a++) {

What is c?

Note also that even a simple char array would fail your first function...

char array [] { 'O', 'o', 'p', 's'  };

[aarg]

You guessed right. The only way the first function can know the length of the array is that the for loop tests for a terminating null. You have to pass the length of the array to the second function.

To trick it into working just for a demo:

unsigned long A[] = { 655390, 1310780, 0 };

... but such a print function couldn't print zeroes.

[Dana1954]

c is a typo, should be a. I simplified the code to bare issue

[alto777]

Your program stopped printing for the same reason the example you worked from.

It printed until it was pointing to some memory that appeared to be 0 when interpreted as a long integer.

So you could do the same thing, put a zero at the end of the kist of values you want to print.

In the case of characters, no one wants or needs to print a character whose value is zero, that’s why it can enjoy special use as a terminator.

You might miss not being able to use 0 when dealing with integers, however.

Sometimes another special value is named, like 9999 as a value never expected to be needed, therefor usable as a flag to mean something different, in this case like you have reached the end of “real” values in a list.

@aarg gmta

a7

[Dana1954]

You're relying on a char string being automatically terminated with a zero byte.
There is no such termination for other arrays.

I see, so length is needed unless 0 could be used as a termination value. I'll pass the length.