Difference between revisions of ";"

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(necessity: wording)
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<div style="float:left; margin: 0 25px 20px 0; padding:50px; font-size:500%; font-family: Georgia; background-color: #f9f9f9; border: 2px solid #777777; clear:both;">;</div>
 
<div style="float:left; margin: 0 25px 20px 0; padding:50px; font-size:500%; font-family: Georgia; background-color: #f9f9f9; border: 2px solid #777777; clear:both;">;</div>
  
The '''semicolon''' <syntaxhighlight lang="pascal" enclose="none">;</syntaxhighlight> is used to ''separate'' statements, in contrast to other programming language where its purpose is to ''terminate'' a statement.
+
The '''semicolon''' <syntaxhighlight lang="pascal" inline>;</syntaxhighlight> is used to
In a block a semicolon without a preceding (qualified) statement indicates an '''empty statement'''.
+
* conclude a [[Declaration|declaration]],
 +
* conclude a constant, <syntaxhighlight lang="delphi" inline>resourceString</syntaxhighlight>, or [[Type|<syntaxhighlight lang="pascal" inline>type</syntaxhighlight>]] definition,
 +
* separate formal parameters in a routine signature,
 +
* separate a routine declaration from its attributes,
 +
* terminate the program header,
 +
* separate alternatives in variant records, and to
 +
* ''separate'' statements, in contrast to other programming language where its purpose is to ''terminate'' a statement.
  
== necessity ==
+
== statement separator ==
 +
=== necessity ===
 
Since language constructs only in their entirety constitute statements, semicolons may not split their components.
 
Since language constructs only in their entirety constitute statements, semicolons may not split their components.
Most notably <syntaxhighlight lang="pascal" enclose="none">;</syntaxhighlight> can not appear immediately before an [[Else|<syntaxhighlight lang="pascal" enclose="none">else</syntaxhighlight>]] that is part of an [[If and Then|<syntaxhighlight lang="pascal" enclose="none">if … then</syntaxhighlight> branch]].
+
Most notably <syntaxhighlight lang="pascal" inline>;</syntaxhighlight> cannot appear immediately before an [[Else|<syntaxhighlight lang="pascal" inline>else</syntaxhighlight>]] that is part of an [[If and Then|<syntaxhighlight lang="pascal" inline>if … then</syntaxhighlight> branch]].
However, <syntaxhighlight lang="pascal" enclose="none">;</syntaxhighlight> in front of an [[End|<syntaxhighlight lang="pascal" enclose="none">end</syntaxhighlight>]] usually is not necessary, but optional and it does not harm insert one anyway.
+
However, <syntaxhighlight lang="pascal" inline>;</syntaxhighlight> in front of an [[End|<syntaxhighlight lang="pascal" inline>end</syntaxhighlight>]] usually is not necessary, but optional and it does not harm insert one anyway.
  
 
As a demonstration, that a single semicolon can make the difference, consider the following listings:
 
As a demonstration, that a single semicolon can make the difference, consider the following listings:
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end;
 
end;
 
</syntaxhighlight>
 
</syntaxhighlight>
If <syntaxhighlight lang="pascal" enclose="none">c</syntaxhighlight> is zero, it remains zero, but becomes <syntaxhighlight lang="pascal" enclose="none">-1</syntaxhighlight> otherwise.
+
If <syntaxhighlight lang="pascal" inline>c</syntaxhighlight> is zero, it remains zero, but becomes <syntaxhighlight lang="pascal" inline>-1</syntaxhighlight> otherwise.
 
<syntaxhighlight lang="pascal" highlight="2">
 
<syntaxhighlight lang="pascal" highlight="2">
 
case c of
 
case c of
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end;
 
end;
 
</syntaxhighlight>
 
</syntaxhighlight>
Here, <syntaxhighlight lang="pascal" enclose="none">c</syntaxhighlight> only becomes <syntaxhighlight lang="pascal" enclose="none">-1</syntaxhighlight> only if it's been zero before.
+
Here, <syntaxhighlight lang="pascal" inline>c</syntaxhighlight> only becomes <syntaxhighlight lang="pascal" inline>-1</syntaxhighlight> if it has been zero before.
As a consequence, and general advice, always put everything in compound statements (i.e. embrace your statements by [[Begin|<syntaxhighlight lang="pascal" enclose="none">begin</syntaxhighlight>]] and <syntaxhighlight lang="pascal" enclose="none">end</syntaxhighlight>) where it's allowed, in order to mitigate such issues.
+
As a consequence, and general advice, always put everything in compound statements (i. e. embrace your statements by [[Begin|<syntaxhighlight lang="pascal" inline>begin</syntaxhighlight>]] and <syntaxhighlight lang="pascal" inline>end</syntaxhighlight>) where it is allowed, in order to mitigate such issues.
 +
{{Note|Using <syntaxhighlight lang="pascal" inline>otherwise</syntaxhighlight> (an [[Extended Pascal]] extension) instead of  <syntaxhighlight lang="delphi" inline>else</syntaxhighlight> in <syntaxhighlight lang="pascal" inline>case</syntaxhighlight>-statements may prevent such mistakes.}}
  
== other remarks ==
+
=== empty statement ===
In the [[ASCII]] character set the semicolon takes the value <syntaxhighlight lang="pascal" enclose="none">59</syntaxhighlight> ([[Hexadecimal|hexadecimal]] <syntaxhighlight lang="delphi" enclose="none">$3B</syntaxhighlight>).
+
In a sequence a semicolon without a preceding (qualified) statement indicates an '''empty statement'''.
  
 
Historically empty statements were used in conjunction with [[Label|labels]].
 
Historically empty statements were used in conjunction with [[Label|labels]].
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If for instance a whole list of statements had to be bypassed, but no qualified statement followed thereafter, the empty statement still provided the possibility.
 
If for instance a whole list of statements had to be bypassed, but no qualified statement followed thereafter, the empty statement still provided the possibility.
  
Also historically, [[Case|<syntaxhighlight lang="pascal" enclose="none">case</syntaxhighlight>-statements]] had to list all possible values the selector variable theoretically could have.
+
Also historically, [[Case|<syntaxhighlight lang="pascal" inline>case</syntaxhighlight>-statements]] had to list all possible values the selector variable theoretically could have.
Now, if a value or range did not imply any action, yet had to be listed inside the <syntaxhighlight lang="pascal" enclose="none">case</syntaxhighlight>-statement in order to fulfill this requirement, an empty statement is the shortest possible way to implement the situation.
+
Now, if a value or range did not imply any action, yet had to be listed inside the <syntaxhighlight lang="pascal" inline>case</syntaxhighlight>-statement in order to fulfill this requirement, an empty statement is the shortest possible way to implement the situation.
 +
 
 +
== other remarks ==
 +
In the [[ASCII]] character set the semicolon takes the value <syntaxhighlight lang="pascal" inline>59</syntaxhighlight> ([[Hexadecimal|hexadecimal]] <syntaxhighlight lang="delphi" inline>$3B</syntaxhighlight>).
  
 
{{Symbols}}
 
{{Symbols}}

Latest revision as of 21:56, 4 July 2021

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;

The semicolon ; is used to

  • conclude a declaration,
  • conclude a constant, resourceString, or type definition,
  • separate formal parameters in a routine signature,
  • separate a routine declaration from its attributes,
  • terminate the program header,
  • separate alternatives in variant records, and to
  • separate statements, in contrast to other programming language where its purpose is to terminate a statement.

statement separator

necessity

Since language constructs only in their entirety constitute statements, semicolons may not split their components. Most notably ; cannot appear immediately before an else that is part of an if  then branch. However, ; in front of an end usually is not necessary, but optional and it does not harm insert one anyway.

As a demonstration, that a single semicolon can make the difference, consider the following listings:

	case c of
		0: if false then c := 42;
		else c := -1;
	end;

If c is zero, it remains zero, but becomes -1 otherwise.

	case c of
		0: if false then c := 42
		else c := -1;
	end;

Here, c only becomes -1 if it has been zero before. As a consequence, and general advice, always put everything in compound statements (i. e. embrace your statements by begin and end) where it is allowed, in order to mitigate such issues.

Note-icon.png

Note: Using otherwise (an Extended Pascal extension) instead of else in case-statements may prevent such mistakes.

empty statement

In a sequence a semicolon without a preceding (qualified) statement indicates an empty statement.

Historically empty statements were used in conjunction with labels. Originally labels can only defined where a statement exists. If for instance a whole list of statements had to be bypassed, but no qualified statement followed thereafter, the empty statement still provided the possibility.

Also historically, case-statements had to list all possible values the selector variable theoretically could have. Now, if a value or range did not imply any action, yet had to be listed inside the case-statement in order to fulfill this requirement, an empty statement is the shortest possible way to implement the situation.

other remarks

In the ASCII character set the semicolon takes the value 59 (hexadecimal $3B).


navigation bar: topic: Pascal symbols
single characters

+ (plus)  •  - (minus)  •  * (asterisk)  •  / (slash)
= (equal)  •  > (greater than)  •  < (less than)
. (period)  •  : (colon)  •  ; (semi colon)
^ (hat)  •  @ (at)
$ (dollar sign)  •  & (ampersand)  •  # (hash)
' (single quote)

character pairs

<> (not equal)  •  <= (less than or equal)  •  := (becomes)  •  >= (greater than or equal)

 •  >< (symmetric difference)  •  // (double slash)