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Active Forums => QB64 Discussion => Topic started by: Dimster on February 09, 2022, 12:23:13 pm

Title: True and False
Post by: Dimster on February 09, 2022, 12:23:13 pm
True and False in QB64 are not key words. At least I don't think they are. They seem to be key words in other languages. In QB64 I can make False = 1 or 10 or 1000 and True = Not False. It seems to me that I need to interpret True or False from the results of an equation. The wiki states True = -1 and False = 0. Quite often I'm not getting those values (particularly for False) even though I know what the correct result of the outcome should be.

True and False seem to be in the background somewhere....If a = 5 then etc ....has a true/false element being performed but we only work with the Then part of the result. I'm wondering, if the STATUS screen at the bottom of the IDE could display decision statements and then either TRUE or FALSE (rather than -1 or 0) to those decision statements in our coding. If not, is it possible to add that feature to Debug in the future?
Title: Re: True and False
Post by: SMcNeill on February 09, 2022, 01:16:56 pm
Quote from: Dimster on February 09, 2022, 12:23:13 pm
The wiki states True = -1 and False = 0. Quite often I'm not getting those values (particularly for False) even though I know what the correct result of the outcome should be.

This isn't quite true with regard to TRUE/FALSE in the BASIC language.

False = 0.   <---   This is our hard and set fact in BASIC.  Zero = FALSE.

**ANYTHING ELSE** = TRUE.

-1 is true.   3 is true.   456.23 is true.   _PI is true.   Anything NOT zero is true.


The reason why people use -1 to represent true, when any value non-zero would work truthfully, is for ease of logical operations.

0 = FALSE
NOT 0 = -1   (NOT FALSE = TRUE)
NOT -1 = 0   (NOT TRUE = FALSE)

Since FALSE is always going to be 0, then NOT FALSE would always be -1.

But as for what's actually evaluated as being a TRUE or FALSE statement, not talking "logical operator based", try out this little program below:

Code: QB64: [Select]
  1. For i = -10 To 10
  2.     Print i;
  3.     If i Then Print "TRUE" Else Print "FALSE"
Title: Re: True and False
Post by: CharlieJV on February 09, 2022, 01:35:15 pm
And now that a proper explanation and example has been given, I am free to throw in and example from the far side:

Code: QB64: [Select]
  1. if len("Paint me green and call me Gumby.") then
  2.     print "TRUE!"
Title: Re: True and False
Post by: Dimster on February 09, 2022, 02:18:08 pm
Steve - Well I have never looked at it from that perspective.

False didn't mean zero, it meant the equation was producing the wrong value. So False had numbers just like your True example values. I'm still thinking (in your example) why i @ 0 isn't TRUE. The loop control values included a zero, so the range of -10 to 10 does include the "value" zero and the loop doesn't appear to me to be a decisional type of statement but rather a simple printing of the index "value"... not a test of True or False???
Title: Re: True and False
Post by: bplus on February 09, 2022, 02:40:13 pm
Code: QB64: [Select]
  1. If i Then Print "TRUE" Else Print "FALSE"
  2.  

Is same as
Code: QB64: [Select]
  1. If i <> 0 Then Print "TRUE" Else Print "FALSE"

IF looks at (value of expression) and THEN takes True path (value <> 0) Else takes False path (value = 0)
Title: Re: True and False
Post by: SMcNeill on February 09, 2022, 02:45:07 pm
Here's a trick when working with IF statements --  Consider them to all have an implied " <> 0 " that they evaluate against.

IF i THEN...

In all truth, the above statement evaluates as if:

IF i <> 0 THEN...     The <> 0 is the implied final comparison.

So when i = -10, the check for -10 <> 0 is true.
when i = -9, the check for -9 <> 0 is true.

When we get down to i = 0, the check for 0 <> 0 is false.


Even if you have a more explicit IF statement, that implied <> 0 is still there at the end.

a = 3
IF a <> 2 THEN  ...

The above gets resolved basically as IF (a <> 2) <> 0 THEN...  (the red is the implied truth check)
a <> 2 becomes 3 <> 2...  that's true, so we have a result of -1.  (The value BASIC returns for truth comparisons.)
-1 <> 0 is true...   So, at the end of the day, a <> 2 is true.


Change the value of a to 2, and we find:

a = 2
IF a <> 2 THEN....

Same as before, the above gets resolved basically as IF (a <> 2) <> 0 THEN...  (the red is the implied truth check)
a <> 2 becomes 2 <> 2...  that's FALSE, so we have a result of 0.  (Remember, in BASIC, FALSE is always ZERO.)
0 <> 0 is false...   So, at the end of the day, a <> 2 is false when a is 2.


All IF statements basically have an implied <> 0 to their evaluation.  When you keep that in mind, the FOR.. NEXT loop which I showed above makes perfect sense.

For i = -10 To 10
    Print i;
    If i <> 0 Then Print "TRUE" Else Print "FALSE"
Next


If it's not false (ZERO), then it's true.  ;)
Title: Re: True and False
Post by: Dimster on February 09, 2022, 03:43:47 pm
Ok, we need to hook up at a bar and have a beer and talk this through.... so you guys are saying the IF is in fact a decision and not a simple ON arriving at the index zero, print the index zero?? The IF statement in your example Steve simply says "IF a", which I have always read "On reaching a " or " If the loop index has reached a .. print it's value"

It seems, even if I make a = 0, which should be a True statement   (ie a = 0  : If a then Print "True" else Print "False" comes up with False)   we don't take away the decisional aspect of "If a"

I appreciate the lesson here. Thanks guys.

Title: Re: True and False
Post by: SMcNeill on February 09, 2022, 03:51:07 pm
Quote from: Dimster on February 09, 2022, 03:43:47 pm
Ok, we need to hook up at a bar and have a beer and talk this through.... so you guys are saying the IF is in fact a decision and not a simple ON arriving at the index zero, print the index zero?? The IF statement in your example Steve simply says "IF a", which I have always read "On reaching a " or " If the loop index has reached a .. print it's value"

It seems, even if I make a = 0, which should be a True statement   (ie a = 0  : If a then Print "True" else Print "False" comes up with False)   we don't take away the decisional aspect of "If a"

I appreciate the lesson here. Thanks guys.

IF a = 0 THEN...

Remember the implied <> 0, which lets us evaluate as

IF (a = 0) <> 0 THEN...

In the case that a = 0, that evaluates as:

a = 0....    Since A is zero, this is true.  We return a -1 to the condition.

Then the implied <> 0 is checked against:

-1 <> 0...   This is true, so the if check gives you a TRUE result and passes.

IF is, in fact, a decision branch.  It evalutes your condition and determines if it's equal to zero (FALSE), or anything else (TRUE).
Title: Re: True and False
Post by: MasterGy on February 09, 2022, 05:50:50 pm
i like to avoid "if" and describe it with action

if a> 5 then b = b +1

this can also be the case:
b = b + abs (a> 5)

an operation can often be expressed faster
Title: Re: True and False
Post by: _vince on February 09, 2022, 05:55:17 pm
Quote from: MasterGy on February 09, 2022, 05:50:50 pm
if a> 5 then b = b +1

this can also be the case:
b = b + abs (a> 5)

nice mod!
Title: Re: True and False
Post by: Dimster on February 10, 2022, 09:49:04 am
@MasterGy ... This is another great example of why True and False become somewhat confusing for me.

I'm going to assume, as in the case of " IF a", the expression ABS(a>5), is also a True and False decision for BASIC, why then if "a" is in fact greater than 5 (being a True statement) is not equal to -1  ??? . This comes back to what Steve was pointing out , that TRUE can be any value except zero. Zero is reserved for FALSE. But in my mind, the math to ABS(a>5) does work out to zero? Why it's calculating to 1 has me stumped. If the variable "a" has not been assigned a value prior to the call to calculate the expression, then it should equate to zero. So we have ABS(0>5) and zero is not greater than 5. Why it calculates to 1 and then determines 1 is TRUE because it not zero

It is only when we start plugging in values for "a" that @ 5 and under we get zero (False) and 6 and up we get 1 (allegedly TRUE), that your formula shines, and thank you for this tip on a work around for IF avoidance. It's just that naked expression ABS(a>5), where no prior value was given for "a" and the naked expression "IF a", where I'm not yet seeing the light. In my mind, those naked expressions should be either -1 or 0 per the conventional values for True and False

 



Title: Re: True and False
Post by: SMcNeill on February 10, 2022, 11:00:40 am
ABS (a > 5)

Remember, with the above, you evaluate what's in parentheses first.

If a is greater than 5, the result is -1. (TRUE)

If a is equal to, or less than 5, the result is 0. (FALSE)

ABS(-1) = 1  -- if a is greater than 5
ABS(0) = 0 -- a less than or equal to 5

So b = b + ABS(a > 5) will only increment the value of b when a is greater than 5.
Title: Re: True and False
Post by: MasterGy on February 10, 2022, 11:01:24 am
It's a lot simpler than you think!

0 is false, and anything that is not 0 is TRUE.

Between the IF and THEN statements, or the condition of the DO-LOOP loop, it does not actually examine a condition, but performs the operation there. If the result of the operation is not zero, i.e. TRUE, it executes the instructions after THEN.

Try !

IF 6> 5 THEN PRINT "TRUE"

and this:

OPERATION = 6> 5
PRINT OPERATION
IF OPERATION THEN PRINT "TRUE"

'OPERATION' will be 0 if the statement is false and -1 if true.
If you start from that, it's easier to see.

"OPERATION =" try several statements and you will understand everything!

operation = 0
operation = -1
operation = 100
operation = (2 and 2)

And such!
Title: Re: True and False
Post by: MasterGy on February 10, 2022, 11:35:44 am
I want to write one more thought that used to confuse me.

IF 6 THEN PRINT "TRUE"

This is okay. 6 is not 0, so it is TRUE, so it executes.

IF 1 THEN PRINT "TRUE"

That's fine too, since 1 isn't 0 either, so it's TRUE.
Both statements are TRUE.

But!
IF 6 AND 1 THEN PRINT "TRUE"
However, it will not do this because 6 AND 1 = 0, so FALSE.

NEVER FORGET ! AND / OR / XOR is a mathematical, logical operation! If there is one in a statement, the program will work with it in a mathematical way, not in a literal interpretation!
Therefore, in such cases, the IF must be supplemented for it to work!
IF SGN (6) AND SGN (1) THEN PRINT "TRUE"
Title: Re: True and False
Post by: Dimster on February 10, 2022, 11:54:08 am
@MasterGy ... that's very interesting and helpful

So, in your first example you have " IF 6 > 5 then Print "True" and sure enough that prints "TRUE" . Why does the reverse of that equation not print FALSE?
IE "IF 6 < 5 then Print "FALSE"

Title: Re: True and False
Post by: MasterGy on February 10, 2022, 12:02:17 pm
you think so, that's right! :)
You have to give it a try and you’ll see that it’s actually a simple thing.
Title: Re: True and False
Post by: SMcNeill on February 10, 2022, 12:02:59 pm
If statements work on truth conditions.

IF (whatever) THEN... only executes what comes next if (whatever) evaluates not equal to zero.

IF 6 < 5 THEN...

6 < 5 is false, so it evaluates to 0, which makes it become

IF 0 THEN...   <-- ZERO says the condition is false; don't execute what comes next.
Title: Re: True and False
Post by: Dimster on February 10, 2022, 12:56:52 pm
As in life, the search for Truth is often elusive. Thanks guys.
Title: Re: True and False
Post by: SMcNeill on February 10, 2022, 01:22:45 pm
I think where you might be having issues is with over thinking things.

Computers aren't LOGICAL things like people are -- they're MATHEMATICAL.

All these issues you're having can be resolved by breaking things down into 2 real processes.


First, is solving an equation until you get a singular result.

a < 5

The above is a math equation, just like 2 + 3, 6 * 4, or SQR(9) are.  In the case of a < 5, the equation can give us 2 results -- -1 if a is less than 5, 0 if it's greater than or equal.

<, >, = are all operators which compare values and return -1 or 0 as a result.

Want to test that?   Just:  PRINT a < 5, and toss various values to a.  The result is going to be -1 or 0.


Now, once you've gotten a singular result, that result determines whether we execute code after an IF statement.

IF (singular result) THEN ....

As long as that (singular result) is ANYTHING BUT ZERO, the code after the IF executes.  If the result is zero, we skip the next block of code.

IF 3 THEN...  <-- 3 isn't 0, so we execute what comes next.

IF 0 THEN...  we don't execute what comes next.


So in the case of "IF a < 6 THEN..."

If a is less than 6, that condition evaluates as:  a < 6 becomes -1.

Substitute that result in the statement and we get:  IF -1 THEN....

Since that final result is ANYTHING BUT ZERO, we execute that IF statement.


Now, in the case that a was greater than 6, it'd evaluate as: a < 6 becomes 0.

Substitute in the IF and we get:  IF 0 THEN...

Since the result is 0, we don't execute the code after that THEN.


Step one is: Resolve the formula to a single result.
Step two is: If that result is zero, skip the code after THEN.


And that's all that's really going on with your true/false checks.  ;)
Title: Re: True and False
Post by: tomxp411 on February 10, 2022, 03:16:19 pm
Quote from: Dimster on February 09, 2022, 03:43:47 pm
Ok, we need to hook up at a bar and have a beer and talk this through.... so you guys are saying the IF is in fact a decision and not a simple ON arriving at the index zero, print the index zero?? The IF statement in your example Steve simply says "IF a", which I have always read "On reaching a " or " If the loop index has reached a .. print it's value"

It seems, even if I make a = 0, which should be a True statement   (ie a = 0  : If a then Print "True" else Print "False" comes up with False)   we don't take away the decisional aspect of "If a"

I appreciate the lesson here. Thanks guys.

You're over-complicating the IF statement.

The IF statement tests for zero. That's all it does. Any other comparisons are actually done by the expression in the IF statement, not IF itself.

IF <value> THEN
<value is not zero>
ELSE
<value is zero>
END IF

IF does not test for equality, greater, lesser, or anything else. It simply checks for zero. In fact, the machine code for this ends up as "Jump if Zero" (JZ) and "Jump if Not Zero" (JNZ).

So everything between IF and THEN is actually an expression., which returns a numeric result.

In BASIC, an expression is basically anything that can be turned into a value: "3" is an expression, "4  + 5" is an expression, and "A < Y" is an expression that returns a Boolean result.

And since a Boolean result is either On or Off, we treat Off as zero and On as -1 (Because signed binary integers are negative when the left bit is on. It's more complicated than that, but that's how the "negative" flag works in machine language.)

So things like IF X=Y are actually two separate operations: the expression (X=Y) is evaluated first and returned as a single value. The IF statement then jumps to the ELSE or END IF when the value is non-zero.

To understand Boolean expressions a bit more, consider these statements:

PRINT 0
PRINT 1
PRINT 0=0
PRINT 0=1
PRINT 1=1

PRINT 0=0 prints -1, because when the = is used in an expression, it's a test for equality. And a test for equality returns -1 when the two values are equal.
Likewise 0=1 returns 0, and 1=1 returns -1

Once you understand the separation between statement and expression, you'll better understand how to use the IF statement to write complex and useful tests.
Title: Re: True and False
Post by: MasterGy on February 10, 2022, 03:24:52 pm
You put it right SMcNeill!

I had similar thoughts, I just couldn’t express myself well.

"SOMETHING ="
After something, there can be functions, operators, relations, equality, whatever. Whatever. If the formula can be evaluated, 'SOMETHING' will have a result. 'IF' has only so much to do with the idea that it executes, if not 0. That's it. The possibilities offered by the programming language must be understood as ‘SOMETHING’ as it can be equal and what are the means by which we can express an idea, a calculation.
Actually, on my own ... I need to be able to play with it. In vain, let us put it according to our own thoughts. No need. You have to try. That’s why I wrote to Dimster to try, play with it, experiment, and when everything becomes clear, he realizes: it’s all simple! but I just complicated it!
Title: Re: True and False
Post by: Dimster on February 10, 2022, 03:40:13 pm
You guys are priceless. Very much appreciate shining a light on this for me.
Title: Re: True and False
Post by: CharlieJV on February 10, 2022, 04:09:14 pm
I find this a terrific thread of discussion.  It makes for excellent documentation.

Do you think it makes sense for me, and/or is it okay, to have added a link to this discussion at the bottom of the Boolean (https://wiki.qb64.org/wiki/Boolean) wiki page ?
Title: Re: True and False
Post by: MasterGy on February 10, 2022, 04:53:53 pm
The beauty of programming. :) when a man grabs the heat and becomes a zombie and is already lazy to press the keyboard, he tries to simplify.

Task: Add all numbers divisible by 3 from 0 to 500 and all numbers divisible by 7 from 500 to 1000, except for square numbers. and except for 35!

Code: QB64: [Select]
  1. 'using IF
  2.  
  3. FOR x = 0 TO 1000
  4.     IF x <> 35 THEN
  5.         IF SQR(x) <> INT(SQR(x)) THEN
  6.             IF x < 500 THEN
  7.                 IF x / 5 = INT(x / 5) THEN sum = sum + x
  8.             ELSE
  9.                 IF x / 7 = INT(x / 7) THEN sum = sum + x
  10.             END IF
  11.         END IF
  12.     END IF
  14. PRINT sum
  15.  
  16. sum = 0
  17.  
  18. 'without IF
  19. FOR x = 0 TO 1000
  20.     sum = sum + ABS(x <> 35 AND SQR(x) <> INT(SQR(x))) * ABS((x < 500) * (x / 5 = INT(x / 5)) + (x > 500) * (x / 7 = INT(x / 7))) * x
  22. PRINT sum
  23.  
  24.  
  25.  

Title: Re: True and False
Post by: SMcNeill on February 10, 2022, 05:10:24 pm
Quote from: MasterGy on February 10, 2022, 04:53:53 pm
The beauty of programming. :) when a man grabs the heat and becomes a zombie and is already lazy to press the keyboard, he tries to simplify.

Task: Add all numbers divisible by 3 from 0 to 500 and all numbers divisible by 7 from 500 to 1000, except for square numbers. and except for 35!

Code: QB64: [Select]
  1. 'using IF
  2.  
  3. FOR x = 0 TO 1000
  4.     IF x <> 35 THEN
  5.         IF SQR(x) <> INT(SQR(x)) THEN
  6.             IF x < 500 THEN
  7.                 IF x / 5 = INT(x / 5) THEN sum = sum + x
  8.             ELSE
  9.                 IF x / 7 = INT(x / 7) THEN sum = sum + x
  10.             END IF
  11.         END IF
  12.     END IF
  14. PRINT sum
  15.  
  16. sum = 0
  17.  
  18. 'without IF
  19. FOR x = 0 TO 1000
  20.     sum = sum + ABS(x <> 35 AND SQR(x) <> INT(SQR(x))) * ABS((x < 500) * (x / 5 = INT(x / 5)) + (x > 500) * (x / 7 = INT(x / 7))) * x
  22. PRINT sum
  23.  
  24.  
  25.  


Code: QB64: [Select]
  1. 'Task: Add all numbers divisible by 3 from 0 to 500 and all numbers divisible by 7 from 500 to 1000, except for square numbers. and except for 35!
  2.  
  3.  
  4. For i = 0 To 500
  5.     sum = sum + Div(i, 3)
  7. For i = 500 To 1000
  8.     sum = sum + Div(i, 7)
  10.  
  11. Print "SUM = "; sum
  12.  
  13. Function Div (num, divisor)
  14.     If Valid(num) And (num Mod divisor = 0) Then Div = num
  16.  
  17. Function Valid (num As Integer)
  18.     If Sqr(num) = Int(Sqr(num)) Then Exit Function
  19.     If num = 35 Then Exit Function
  20.     Valid = -1
Title: Re: True and False
Post by: MasterGy on February 10, 2022, 05:29:19 pm
This is it !!! ! beautiful ! compression and elegance! this is the attitude of programming! :)))))
Title: Re: True and False
Post by: Dimster on February 13, 2022, 12:04:57 pm
Hey @MasterGy ... when I asked you why 6 < 5 did not print 0 (or False) and the explanation was revealed that the IF evaluation wouldn't go to any instructions after evaluating the first part to zero....well it seems if you use an ELSE in the IF statement you can get it to print the zero (or False)

If 6 > 5 then print 6 > 5 Else print 6 >5 ... this results in -1 printed to the screen
if 6 < 5 then print 6 < 5 Else print 6<5 ... this results in 0 printed to the screen
so could also ask it to print True or False and it works.

I'm going to start to incorporate this double choice in resultants and see if this helps or hinders. As I had mentioned, I seems to be getting a lot of miss reads especially on False. The explanation on how IF is actually looking for zero sure did turn a light on.
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