Difference between revisions of "Basic Pascal Tutorial/Chapter 3/WHILE..DO"
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The pretest loop has the following format: | The pretest loop has the following format: | ||
| − | < | + | <syntaxhighlight> |
while BooleanExpression do | while BooleanExpression do | ||
statement; | statement; | ||
| − | </ | + | </syntaxhighlight> |
The loop continues to execute until the Boolean expression becomes <tt>FALSE</tt>. In the body of the loop, you must somehow affect the Boolean expression by changing one of the variables used in it. Otherwise, an infinite loop will result: | The loop continues to execute until the Boolean expression becomes <tt>FALSE</tt>. In the body of the loop, you must somehow affect the Boolean expression by changing one of the variables used in it. Otherwise, an infinite loop will result: | ||
| − | < | + | <syntaxhighlight> |
a := 5; | a := 5; | ||
while a < 6 do | while a < 6 do | ||
writeln (a); | writeln (a); | ||
| − | </ | + | </syntaxhighlight> |
Remedy this situation by changing the variable's value: | Remedy this situation by changing the variable's value: | ||
| − | < | + | <syntaxhighlight> |
a := 5; | a := 5; | ||
while a < 6 do | while a < 6 do | ||
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a := a + 1 | a := a + 1 | ||
end; | end; | ||
| − | </ | + | </syntaxhighlight> |
The <tt>WHILE ... DO</tt> loop is called a pretest loop because the condition is tested before the body of the loop executes. So if the condition starts out as <tt>FALSE</tt>, the body of the <tt>while</tt> loop never executes. | The <tt>WHILE ... DO</tt> loop is called a pretest loop because the condition is tested before the body of the loop executes. So if the condition starts out as <tt>FALSE</tt>, the body of the <tt>while</tt> loop never executes. | ||
Revision as of 16:07, 24 March 2012
3Db - WHILE..DO (author: Tao Yue, state: unchanged)
The pretest loop has the following format:
while BooleanExpression do
statement;The loop continues to execute until the Boolean expression becomes FALSE. In the body of the loop, you must somehow affect the Boolean expression by changing one of the variables used in it. Otherwise, an infinite loop will result:
a := 5;
while a < 6 do
writeln (a);Remedy this situation by changing the variable's value:
a := 5;
while a < 6 do
begin
writeln (a);
a := a + 1
end;The WHILE ... DO loop is called a pretest loop because the condition is tested before the body of the loop executes. So if the condition starts out as FALSE, the body of the while loop never executes.
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