如何将此循环限制为特定数字？

below is from part of a loop

foreach($dataSet as $cType => $cPercentage){ echo $cType ."=". $cPercentage; }

this out put datas depend on array. what I want is I want to run this loop to only a particular number of times. say 8 times.

$nLoop = 0;
foreach($dataSet as $cType => $cPercentage){
  if ($nLoop++ == 8)
    break;
  echo $cType ."=". $cPercentage;
}

If you mean by "to a number", do you mean like "8 times"? That you could do by

 $i=0;   
foreach($dataSet as $cType => $cPercentage){
    if($i==8){break;} 
    $i++;
    echo $cType ."=". $cPercentage; 
}

This should work for numeric & associative arrays

$count = 0;
foreach($dataSet as $cType => $cPercentage) {
    echo $cType ."=". $cPercentage;
    if (++$count > 8) break;
}

Possibly, but not real advantage

$cappedArray = array_slice($dataSet, 0, 8, true);
foreach($cappedArray as $cType => $cPercentage) {
    echo $cType ."=". $cPercentage;
}

you can use the for loop to do this for you

Try a while loop

$i = 0;
while($ds = each($dataSet) && $i < 8) {
   echo $ds['key']. '='.$ds['value'];
   $i++;
}

You can also use another type of loop, e.g. while:

reset($dataSet);
$i = 8;
while((list($cType, $cPercentage) = each($dataSet)) && $i--) {
    echo $cType, ."=". $cPercentage;
}
reset($dataSet);

Reference: reset, each, list

Explanation:

each returns the key and value of the item the internal array pointer points to as array and advances the internal pointer. list assignes the array of key and value to two variables and returns the array. $i-- decrements the counter variable.
The loop will stop if either there are no elements in the array anymore (thus the array implicitly returned by list will be empty and evaluate to false) or if $i is 0.

If you want to truncate size of array you can use array_slice

so your code would look like this:

foreach(array_slice($dataSet, 0, 8) as $cType => $cPercentage){ echo $cType ."=". $cPercentage; }