on what occasion it can be used

[Kiara87]

hi all I saw an instruction that changes a variable and is called
swap variable
then I noticed that you can also create it without swap
leaning on a third variable making a transfer of variable

uno$ = "buon"
due$ = "giorno"


tre$ = uno$
uno$ = due$
due$ = tre$


PRINT uno$, uno$
PRINT due$, due$

invece swap

a$ = "one"
b$ = "two"

SWAP a$, b$

PRINT a$
PRINT b$


my question and what can make this change useful for?

if you want to write a variable you can write one first and after the other there would be no need to change?
someone to an example of some program to make me understand why this can be useful?

[bplus]

Very often used in sorting where you want to switch the values of 2 array items so they will be in alphabetic order.

Have you ever tried making a little sort routine?

[Pete]

Quick... Someone get Steve a bucket!

Code: QB64: [Select]

1. REM SWAP demo to alphabetize a list...
2. myarray$(1) = "dog"
3. myarray$(2) = "cat"
4. myarray$(3) = "rabbit"
5. myarray$(4) = "frog"
6. myarray$(5) = "horse"
7. h = 5
8. FOR i = 1 TO h
9.     FOR j = 1 TO h
10.         IF i <> j THEN
11.             IF myarray$(i) < myarray$(j) THEN SWAP myarray$(i), myarray$(j)
12.         END IF
13. NEXT j, i
14.  
15. FOR i = 1 to h
16. PRINT myarray$(i)
17. NEXT
18.  

Pete

[_vince]

Mainly convenience, you also avoid creating a new variable tre$ which compromises code readability and possibly memory usage.

Also, some computers are faster at swapping things than copying things, this lets them know that what you really want is a mere swap which they are much more eager to perform.

Code: QB64: [Select]

1. un$ = "palpiti"
2. dos$ = "sentir "
3.  
4.  
5. ? un$, dos$
6.  
7. for i=1 to len(un$)
8.         un$ = mid$(un$,1,i-1)+chr$(asc(mid$(un$, i, 1)) xor asc(mid$(dos$, i, 1)))+mid$(un$,i+1, len(un$)-1)
9.         dos$ = mid$(dos$,1,i-1)+chr$(asc(mid$(dos$, i, 1)) xor asc(mid$(un$, i, 1)))+mid$(dos$,i+1, len(dos$)-1)
10.         un$ = mid$(un$,1,i-1)+chr$(asc(mid$(un$, i, 1)) xor asc(mid$(dos$, i, 1)))+mid$(un$,i+1, len(un$)-1)
11. next
12.  
13. ? un$, dos$
14.  
15. sleep
16. system
17.  

[Kiara87]

thank you all
I understood that it also recognizes letters if they are major or minor as in the example below
example recognizes that a is less than b and b is less than c

Code: QB64: [Select]

1. REM SWAP demo TO alphabetize a LIST...
2. myarray$(1) = "aa"
3. myarray$(2) = "ab"
4. myarray$(3) = "ac"
5. myarray$(4) = "ad"
6. myarray$(5) = "af"
7. myarray$(6) = "ag"
8. myarray$(7) = "ah"
9. myarray$(8) = "ai"
10. myarray$(9) = "al"
11. myarray$(10) = "am"
12.  
13.  
14.  
15.  
16.  
17. h = 10
18. FOR i = 1 TO h
19.     FOR j = 1 TO h
20.         IF i <> j THEN
21.             IF myarray$(i) < myarray$(j) THEN SWAP myarray$(i), myarray$(j)
22.         END IF
23. NEXT j, i
24.  
25. FOR i = 1 TO h
26.     PRINT myarray$(i)
27.  
28. NEXT

another question because the for loop only gets to 10 if I go beyond it doesn't go anymore

like in this example?

Code: QB64: [Select]

1. REM SWAP demo TO alphabetize a LIST...
2. myarray$(1) = "aa"
3. myarray$(2) = "ab"
4. myarray$(3) = "ac"
5. myarray$(4) = "ad"
6. myarray$(5) = "af"
7. myarray$(6) = "ag"
8. myarray$(7) = "ah"
9. myarray$(8) = "ai"
10. myarray$(9) = "al"
11. myarray$(10) = "am"
12. myarray$(11) = "ao"
13.  
14.  
15.  
16.  
17. h = 11
18. FOR i = 1 TO h
19.     FOR j = 1 TO h
20.         IF i <> j THEN
21.             IF myarray$(i) < myarray$(j) THEN SWAP myarray$(i), myarray$(j)
22.         END IF
23. NEXT j, i
24.  
25. FOR i = 1 TO h
26.     PRINT myarray$(i)
27.  
28. NEXT

so i can't get from a to z ?

thanks

[bplus]

You have to DIM an array > 10

ie DIM MyArray$(1 to 11)

fixed

Code: QB64: [Select]

1. REM SWAP demo TO alphabetize a LIST...
2.  
3. DIM myArray$(1 TO 11)
4. myArray$(1) = "aa"
5. myArray$(2) = "Ab"
6. myArray$(3) = "ac"
7. myArray$(4) = "ad"
8. myArray$(5) = "af"
9. myArray$(6) = "Ag"
10. myArray$(7) = "ah"
11. myArray$(8) = "ai"
12. myArray$(9) = "al"
13. myArray$(10) = "am"
14. myArray$(11) = "Ao"
15.  
16.  
17.  
18.  
19. h = UBOUND(myArray$)
20. FOR i = 1 TO h - 1 '<<<<<<<<<<<< fix for slightly better code
21.     FOR j = i + 1 TO h '<<<<<<<< fix so j <> i ever
22.         'IF i <> j THEN    i <> j always!!!
23.         IF myArray$(i) > myArray$(j) THEN SWAP myArray$(i), myArray$(j) ' descending switch < to >
24.         'END IF
25. NEXT j, i
26.  
27. FOR i = 1 TO h
28.     PRINT myArray$(i)
29.  
30. NEXT
31.  
32.  

If you have to sort a much bigger array you might want something faster than this, but fine for little arrays.

[Pete]

10 arrays ought to be enough for anybody... B.G.

[bplus]

Arrays the extra then ;-))

[OldMoses]

10 arrays ought to be enough for anybody... B.G.

Many moons ago, Ten Arrays put on his war paint and met Loops While True in single combat. The battle was long and GUI.

[Pete]

Now that's a post that deserves many moons. It's getting one from me right now. Oops, wrong forum, I'm Skyping on the Oprah Forum. Sorry ladies.

Pete

[TempodiBasic]

@Kiara87
hi
here an example of using Swap for graphic values

Code: QB64: [Select]

1. 'impostare una finestra grafica/ set a graphic window
2. SCREEN _NEWIMAGE(800, 600, 32)
3. ' imposta il nome finestra / set name of window
4. _TITLE "OpenGL 1"
5.  
6. ' costanti generali / general constants
7. CONST True = -1, False = 0
8.  
9. ' constanti colori / colors constants
10. CONST Black = _RGBA32(0, 0, 0, 255), White = _RGBA32(255, 255, 255, 255)
11. ' variabili/ variables
12. DIM Kb AS INTEGER, Done AS INTEGER
13. DIM SHARED FS AS INTEGER, Init AS INTEGER
14. DIM SHARED Gc AS SINGLE, Rc AS SINGLE, Bc AS SINGLE, Gc1 AS SINGLE, Rc1 AS SINGLE, Bc1 AS SINGLE
15. 'inizializzazione delle variabili /initalitation of variables
16. FS = True
17. Init = True
18. Kb = 0
19. Done = False
20.  
21. Rc = 1.0: Gc = 1.0: Bc = 0.0: Rc1 = 0.0: Gc1 = 1.0: Bc1 = 1.0
22. ' ciclo principale /main loop
23. DO
24.     ' area di ingresso dati /area of input
25.     Kb = _KEYHIT
26.     ' traduttore dei comandi dati con tastiera/ translator commands given by keyboard
27.     IF Kb THEN
28.         ' se barra spazio cambio lo stato di FS
29.         IF Kb = 32 THEN
30.             FS = NOT FS
31.             Init = True
32.         END IF
33.         IF Kb = 27 THEN Done = True
34.         IF Kb = 13 THEN
35.             SWAP Gc, Gc1
36.             SWAP Bc, Bc1
37.             SWAP Rc, Rc1
38.         END IF
39.     END IF
40.     ' esecutore dei comandi individuati dal traduttore comandi
41.     ' executor of commands taken from  commands of translator
42.     IF FS = True THEN
43.         _FULLSCREEN
44.     ELSE
45.         _FULLSCREEN OFF
46.     END IF
47. LOOP UNTIL Done = True
48. END ' fine logica del programma / logical end of the program
49.  
50.  
51. '----Area Subroutines and Functions--------
52.  
53. SUB _GL ()
54.     'qui vanno tutte le istruzioni _gl / here all _gl instructions
55.     IF Init THEN
56.         ' area di inizializzazione/initialization area
57.  
58.         ' se  e' schermo intero imposta l'intero schermo come viewport
59.         ' if it is  full screen it sets whole screen as viewport
60.  
61.         IF FS THEN
62.             _glViewport 0, 0, _WIDTH, _HEIGHT
63.         ELSE
64.             ' se non e' schermo intero imposta il quarto in basso a destra come viewport
65.             ' if it is not full screen  it sets the quarter at bottom right as viewport
66.             _glViewport _WIDTH / 2, _HEIGHT / 2, _WIDTH, _HEIGHT
67.         END IF
68.  
69.         _glClearColor 0.7, 0.0, 0.0, 1.0 ' colore sfondo / background
70.         Init = False ' disattiva il flag  / it disactivates the flag
71.         'END IF
72.     ELSE
73.         _glClear (_GL_COLOR_BUFFER_BIT OR _GL_DEPTH_BUFFER_BIT) ' rigenera il color buffer bit / it clear color buffer bit
74.  
75.  
76.         IF FS THEN
77.             ' esegue a tutto schermo/ it executes in fullscreen mode
78.             _glBegin _GL_LINE_LOOP
79.             _glColor3f Rc, Gc, Bc
80.             _glVertex3d -1.0, -1.0, 0.0
81.             _glVertex3d 0.0, 1.0, 0.0
82.             _glVertex3d -0.0, -0.5, 0.0
83.             _glEnd
84.         ELSE
85.             ' esegue a finestra / it executes in window mode
86.             _glBegin _GL_LINE_STRIP
87.             _glColor3f Rc1, Gc1, Bc1
88.             _glVertex3d 0.0, 0.0, 0.0
89.             _glVertex3d 1.0, -0.6, -0.7
90.             _glVertex3d 1.0, 0.0, 0.0
91.             _glVertex3d 0.0, -0.6, -0.7
92.             _glEnd
93.         END IF
94.         _glFlush
95.     END IF
96.  
97. END SUB

every time you press Enter you change the color of the lines drawn... with Spacebar you change the mode and the lines that you can see, and at the end Escape let you quit the program.
You save to typing more code and save RAM creating less variables as our friends has shown you above.

[bplus]

I just used SWAP here: https://www.qb64.org/forum/index.php?topic=3053.msg123250#msg123250

To select the lesser of two random picked x, y coordinates for a top left corner of a box, and the other random picked x, y for the bottom right corner of a box which needed a greater x and y than used in top left corner.

[SMcNeill]

To address the simplest answer:

Swap *never* has to be used.  If you want to trade values from X and Y, you can *always* use a temp variable as the go between to do so.

temp = X
X = Y
Y = temp

So why *would* you ever want to use SWAP?

1) Readability.  Once you’re used to the command, it’s simply reading and deciphering one single, self-documenting function, in your code.

2) Reduced typing.  With expressive character names, or types, it’s much quicker and less strain than typing multiple variables names over and over.  Without using SWAP, you type those variable names six times.  With it, you only type them twice.  Reduce repetitive stress as much as possible — your joints will thank you for it later!

3) Less memory usage and program overhead.  Adding a temp variable means allocating the memory for that variable.  Now, on modern 128GB systems, 4-bytes isn’t anything to care about, but it’s never a good practice to get into making bloatware.  Who knows what microprocessor/system you’ll want to code on in the future?

SWAP *never* has to be used, but generally speaking, it *should* generally be your goto method for swapping two values.  When you can use it, use it.  Honestly, it doesn’t make any sense not to, that I know of.

Can anyone out there think of a time/reason when it’d be best to use a temp variable as a middleman and manually do the process, ratherthan just use SWAP?  I’m honestly drawing a blank on why one wouldn’t use it, when they could.

[Pete]

Can anyone out there think of a time/reason when it’d be best to use a temp variable as a middleman and manually do the process, ratherthan just use SWAP?  I’m honestly drawing a blank on why one wouldn’t use it, when they could.

Yes, dammit, because some of us like doing everything the hard way!!!!!!

Pete :D

[Kiara87]

obviously it doesn't make sense to use a temporary variable

since there is education

which changes the variable automatically

thank

To address the simplest answer:

Swap *never* has to be used.  If you want to trade values from X and Y, you can *always* use a temp variable as the go between to do so.

temp = X
X = Y
Y = temp

So why *would* you ever want to use SWAP?

1) Readability.  Once you’re used to the command, it’s simply reading and deciphering one single, self-documenting function, in your code.

2) Reduced typing.  With expressive character names, or types, it’s much quicker and less strain than typing multiple variables names over and over.  Without using SWAP, you type those variable names six times.  With it, you only type them twice.  Reduce repetitive stress as much as possible — your joints will thank you for it later!

3) Less memory usage and program overhead.  Adding a temp variable means allocating the memory for that variable.  Now, on modern 128GB systems, 4-bytes isn’t anything to care about, but it’s never a good practice to get into making bloatware.  Who knows what microprocessor/system you’ll want to code on in the future?

SWAP *never* has to be used, but generally speaking, it *should* generally be your goto method for swapping two values.  When you can use it, use it.  Honestly, it doesn’t make any sense not to, that I know of.

Can anyone out there think of a time/reason when it’d be best to use a temp variable as a middleman and manually do the process, ratherthan just use SWAP?  I’m honestly drawing a blank on why one wouldn’t use it, when they could.