mirror of
https://github.com/QB64Official/qb64.git
synced 2024-08-31 13:30:15 +00:00
127 lines
5.4 KiB
Text
127 lines
5.4 KiB
Text
|
The {{KW|SWAP}} statement is used to exchange two variable or array element values.
|
||
|
|
||
|
|
||
|
{{PageSyntax}}
|
||
|
:{{KW|SWAP}} {{Parameter|variable1}}, {{Parameter|variable2}}
|
||
|
|
||
|
|
||
|
{{PageDescription}}
|
||
|
|
||
|
* {{Parameter|variable1}} and {{Parameter|variable2}} are any type variables whose values will be exchanged.
|
||
|
* If either {{Parameter|variable1}} or {{Parameter|variable2}} is an array, then an element in the array must be designated.
|
||
|
* {{KW|SWAP}} can be used with string or number variable values. Both must be of the same type.
|
||
|
* It is often used to sort array elements into greater or lesser values.
|
||
|
* SWAP can be used in page flipping to change between 2 page numbers.
|
||
|
|
||
|
|
||
|
''Example 1:'' A simple SWAP of [[STRING|string]] values.
|
||
|
{{CodeStart}}
|
||
|
a$ = "one"
|
||
|
b$ = "two"
|
||
|
|
||
|
{{Cl|SWAP}} a$, b$
|
||
|
|
||
|
{{Cl|PRINT}} a$
|
||
|
{{Cl|PRINT}} b$
|
||
|
{{CodeEnd}}
|
||
|
{{OutputStart}}two
|
||
|
one
|
||
|
{{OutputEnd}}
|
||
|
|
||
|
|
||
|
''Example 2:'' Creating Cryptograms by scrambling EVERY capital letter in the alphabet.
|
||
|
{{CodeStart}} '' ''
|
||
|
{{Cl|DIM}} Letter$(65 {{Cl|TO}} 90)
|
||
|
{{Cl|RANDOMIZE}} {{Cl|TIMER}}
|
||
|
{{Cl|CLS}}
|
||
|
{{Cl|FOR...NEXT|FOR}} a = 65 {{Cl|TO}} 90 'set ASCII codes and letters in order
|
||
|
Letter$(a) = {{Cl|CHR$}}(a) 'create capitalized characters
|
||
|
{{Cl|NEXT}} a
|
||
|
|
||
|
{{Cl|COLOR}} 11: {{Cl|LOCATE}} 10, 10
|
||
|
{{Cl|FOR...NEXT|FOR}} i = 65 {{Cl|TO}} 90
|
||
|
{{Cl|IF...THEN|IF}} Letter$(i) = {{Cl|CHR$}}(i) {{Cl|THEN}} 'find characters the same as the {{Cl|ASCII}} code index
|
||
|
{{Cl|DO...LOOP|DO}}: j = {{Cl|INT}}({{Cl|RND}} * 26) + 65: {{Cl|LOOP}} {{Cl|WHILE}} j = i 'loop until j <> i
|
||
|
{{Cl|SWAP}} Letter$(i), Letter$(j) 'swap corresponding letter characters
|
||
|
{{Cl|END IF}}
|
||
|
{{Cl|PRINT}} {{Cl|CHR$}}(i); " "; 'print normal alphabetical order
|
||
|
{{Cl|NEXT}}
|
||
|
|
||
|
{{Cl|COLOR}} 14: {{Cl|LOCATE}} 12, 10
|
||
|
{{Cl|FOR...NEXT|FOR}} a = 65 {{Cl|TO}} 90 'display new alphabetical order
|
||
|
{{Cl|PRINT}} Letter$(a); " ";
|
||
|
{{Cl|NEXT}}
|
||
|
|
||
|
text$ = "This is how a normal sentence would look before being encrypted."
|
||
|
{{Cl|COLOR}} 11: {{Cl|LOCATE}} 20, 5: {{Cl|PRINT}} text$
|
||
|
L = {{Cl|LEN}}(text$)
|
||
|
{{Cl|DIM}} Code(L) 'place ASCII code solution into an array
|
||
|
{{Cl|COLOR}} 14: {{Cl|LOCATE}} 22, 5
|
||
|
{{Cl|FOR...NEXT|FOR}} i = 1 {{Cl|TO}} L
|
||
|
Code(i) = {{Cl|ASC}}({{Cl|UCASE$}}(text$), i) 'in QB64, ASC can read by character position
|
||
|
{{Cl|IF...THEN|IF}} Code(i) >= 65 {{Cl|AND (boolean)|AND}} Code(i) <= 90 {{Cl|THEN}} {{Cl|PRINT}} Letter$(Code(i)); {{Cl|ELSE}} {{Cl|PRINT}} {{Cl|CHR$}}(Code(i));
|
||
|
{{Cl|NEXT}}
|
||
|
{{Cl|END}} '' ''
|
||
|
{{CodeEnd}}
|
||
|
{{small|Code by Ted Weissgerber}}
|
||
|
:'' Explanation:'' The Letter$ [[STRING]] [[Arrays|array]] is first created with the letters matching the [[ASCII]] code index value. Every index is '''swap'''ped when the letter matches it's index code until every letter is different. The Code array holds the text code solution.
|
||
|
|
||
|
|
||
|
''Example 3:'' A very quick array sorting SUB procedure using recursion sorts 10 thousand numbers in milliseconds.
|
||
|
{{CodeStart}} '' ''
|
||
|
{{Cl|DEFINT}} A-Z
|
||
|
{{Cl|DIM}} {{Cl|SHARED}} swap2 {{Cl|AS}} {{Cl|LONG}} 'Demo only
|
||
|
{{Cl|DIM}} array(10000) {{Cl|AS}} {{Cl|SINGLE}} 'array can hold any type of value
|
||
|
{{Cl|RANDOMIZE}} {{Cl|TIMER}}
|
||
|
{{Cl|FOR...NEXT|FOR}} i = 0 {{Cl|TO}} 10000
|
||
|
array(i) = {{Cl|RND}} * 1000 'populate array with random values to sort
|
||
|
{{Cl|NEXT}}
|
||
|
start = {{Cl|LBOUND}}(array) 'lowest element
|
||
|
finish = {{Cl|UBOUND}}(array) 'highest element
|
||
|
swap2 = 0 'count swaps for demo only
|
||
|
start! = {{Cl|TIMER}}(.001)
|
||
|
{{Cl|CALL}} QuickSort(start, finish, array())
|
||
|
ending! = {{Cl|TIMER}}(.001)
|
||
|
tmp$ = " array(0)= ##.##### array(5000)= ###.#### array(10000)= ###.####"
|
||
|
{{Cl|PRINT USING}} tmp$; array(0); array(5000); array(10000)
|
||
|
{{Cl|PRINT USING}} " Elapsed time: #.###### seconds with #######, swaps"; ending! - start!; swap2&
|
||
|
{{Cl|FOR...NEXT|FOR}} n = 0 {{Cl|TO}} 10000 'check array sort order
|
||
|
{{Cl|IF}} array(n) >= max! {{Cl|THEN}} 'max should match the array type
|
||
|
max! = array(n)
|
||
|
{{Cl|ELSE}} {{Cl|BEEP}}
|
||
|
{{Cl|PRINT}} "Bad sort order!"
|
||
|
{{Cl|EXIT}} {{Cl|FOR...NEXT|FOR}}
|
||
|
{{Cl|END IF}}
|
||
|
{{Cl|NEXT}}
|
||
|
{{Cl|END}}
|
||
|
|
||
|
{{Cl|SUB}} QuickSort (start {{Cl|AS}} {{Cl|INTEGER}}, finish {{Cl|AS}} {{Cl|INTEGER}}, array() {{Cl|AS}} {{Cl|SINGLE}})
|
||
|
{{Cl|DIM}} Hi {{Cl|AS}} {{Cl|INTEGER}}, Lo {{Cl|AS}} {{Cl|INTEGER}}, Middle {{Cl|AS}} {{Cl|SINGLE}}
|
||
|
Hi = finish: Lo = start
|
||
|
Middle = array((Lo + Hi) / 2) 'find middle of array
|
||
|
{{Cl|DO}}
|
||
|
{{Cl|DO}} {{Cl|WHILE}} array(Lo) < Middle: Lo = Lo + 1: {{Cl|LOOP}}
|
||
|
{{Cl|DO}} {{Cl|WHILE}} array(Hi) > Middle: Hi = Hi - 1: {{Cl|LOOP}}
|
||
|
{{Cl|IF}} Lo <= Hi {{Cl|THEN}}
|
||
|
{{Cl|SWAP}} array(Lo), array(Hi)
|
||
|
swap2 = swap2 + 1 'count swaps for demo only
|
||
|
Lo = Lo + 1: Hi = Hi - 1
|
||
|
{{Cl|END IF}} 'If homework, you will fail
|
||
|
{{Cl|LOOP}} {{Cl|UNTIL}} Lo > Hi
|
||
|
{{Cl|IF}} Hi > start {{Cl|THEN}} {{Cl|CALL}} QuickSort(start, Hi, array())
|
||
|
{{Cl|IF}} Lo < finish {{Cl|THEN}} {{Cl|CALL}} QuickSort(Lo, finish, array())
|
||
|
{{Cl|END SUB}} '' ''
|
||
|
{{CodeEnd}}
|
||
|
{{OutputStart}} array(0)= 0.20200 array(5000)= 525.8505 array(10000)= 999.6196
|
||
|
Elapsed time: 0.023438 seconds with 33,759 swaps
|
||
|
{{OutputEnd}}
|
||
|
:'''NOTE:''' The ''swap2'' shared value is used to count the swaps for the demo and can be removed from the SUB procedure for speed.
|
||
|
|
||
|
|
||
|
''See also:''
|
||
|
* [[RND]], [[RANDOMIZE]]
|
||
|
* [[CHR$]], [[ASC]]
|
||
|
* [[ASCII]], [[Arrays]]
|
||
|
|
||
|
|
||
|
{{PageNavigation}}
|