Editing C syntax (section)

===Iteration statements===
C has three forms of [[iteration]] statement:
<syntaxhighlight lang=C>
do
    <statement>
while ( <expression> ) ;

while ( <expression> )
    <statement>

for ( <expression> ; <expression> ; <expression> )
    <statement>
</syntaxhighlight>

In the [[while loop|{{code|while}}]] and {{code|do}} statements, the sub-statement is executed repeatedly so long as the value of the {{code|expression}} remains non-zero (equivalent to true). With {{code|while}}, the test, including all side effects from {{code|<expression>}}, occurs before each iteration (execution of {{code|<statement>}}); with {{code|do}}, the test occurs after each iteration. Thus, a {{code|do}} statement always executes its sub-statement at least once, whereas {{code|while}} may not execute the sub-statement at all.

The statement:
<syntaxhighlight lang=C>
for (e1; e2; e3)
    s;
</syntaxhighlight>
is equivalent to:
<syntaxhighlight lang=C>
e1;
while (e2)
{
    s;
cont:
    e3;
}
</syntaxhighlight>
except for the behaviour of a {{code|continue;}} statement (which in the {{code|for}} loop jumps to {{code|e3}} instead of {{code|e2}}). If {{code|e2}} is blank, it would have to be replaced with a {{code|1}}.

Any of the three expressions in the {{code|for}} loop may be omitted. A missing second expression makes the {{code|while}} test always non-zero, creating a potentially infinite loop.

Since [[C99]], the first expression may take the form of a declaration, typically including an initializer, such as:
<syntaxhighlight lang=C>
for (int i = 0; i < limit; ++i) {
    // ...
}
</syntaxhighlight>

The declaration's scope is limited to the extent of the {{code|for}} loop.