Editing Infinite loop (section)

==Pseudo-infinite loops==
A pseudo-infinite loop is a loop that appears infinite but is really just a very long loop.

===Very large numbers===
An example in [[Bash (Unix shell)|bash]]:
<syntaxhighlight lang="bash">
for x in $(seq 1000000000); do
#loop code
done
</syntaxhighlight>

===Impossible termination condition===
An example [[for loop]] in [[C (programming language)|C]]:
<syntaxhighlight lang="c">
unsigned int i;
for (i = 1; i != 0; i++) {
  /* loop code */
}
</syntaxhighlight>
It appears that this will go on indefinitely, but in fact the value of <code>i</code> will eventually reach the maximum value storable in an <code>unsigned int</code> and adding 1 to that number will wrap-around to 0, breaking the loop. The actual limit of <code>i</code> depends on the details of the system and [[compiler]] used. With [[arbitrary-precision arithmetic]], this loop would continue until the computer's [[memory (computers)|memory]] could no longer hold <code>i</code>. If <code>i</code> was a signed integer, rather than an unsigned integer, overflow would be undefined. In this case, the compiler could optimize the code into an infinite loop.

===Infinite recursion===
{{Main|Recursion (computer science)#Infinite recursion}}
Infinite recursion is a special case of an infinite loop that is caused by [[recursion (computer science)|recursion]]. 

The following example in [[Visual Basic for Applications]] (VBA) returns a [[stack overflow]] error:
<syntaxhighlight lang="vbscript">
Sub Test1()
    Call Test1
End Sub
</syntaxhighlight>

===Break statement===
A "<code>while (true)</code>" loop looks infinite at first glance, but there may be a way to escape the loop through a [[break statement]] or [[return statement]].
Example in [[PHP]]:
<syntaxhighlight lang="php">
while (true) {
    if ($foo->bar()) {
        return;
    }
}
</syntaxhighlight>

===Alderson loop===
''Alderson loop'' is a rare slang or [[The Jargon File|jargon]] term for an infinite loop where there is an exit condition available, but inaccessible in an implementation of the code, typically due to a programmer error. These are most common and visible while [[debugging]] [[user interface]] code.

A C-like pseudocode example of an Alderson loop, where the program is supposed to sum numbers given by the user until zero is given, but where the wrong operator is used:
<syntaxhighlight lang="C">
int sum = 0;
int i;
while (true) {
   printf("Input a number to add to the sum or 0 to quit");
   i = getUserInput();
   if (i * 0) { // if i times 0 is true, add i to the sum. Note: ZERO means FALSE, Non-Zero means TRUE. "i * 0" is ZERO (FALSE)!
      sum += i; // sum never changes because (i * 0) is 0 for any i; it would change if we had != in the condition instead of *
   }
   if (sum > 100) {
      break;    // terminate the loop; exit condition exists but is never reached because sum is never added to
   }
}
</syntaxhighlight>

The term allegedly received its name from a programmer (whose last name is Alderson) who in 1996<ref>{{cite web
 |url=https://www.lee-dohm.com/2013/05/24/alderson-loop
 |title=Alderson loop
 |author=Lee Dohm
 |date=May 24, 2013
 |access-date=January 22, 2020
 |archive-date=June 19, 2020
 |archive-url=https://web.archive.org/web/20200619200434/https://www.lee-dohm.com/2013/05/24/alderson-loop/
 |url-status=live
 }}</ref> had coded a [[modal window|modal]] [[dialog box]] in [[Microsoft Access]] without either an OK or Cancel button, thereby disabling the entire program whenever the box came up.<ref>{{Cite web |url=http://www.catb.org/~esr/jargon/html/A/Alderson-loop.html |title=Alderson Loop |website=[[The Jargon File]], Version 4.4.7 |url-status=live |archive-url=https://web.archive.org/web/20060515053043/http://www.catb.org/~esr/jargon/html/A/Alderson-loop.html |archive-date=2006-05-15 |access-date=2006-05-21}}</ref>