PHP basic array

This article mainly introduces the basic array of PHP, which has certain reference value. Now I share it with everyone. Friends in need can refer to it

Array definition

$arr = array("a","b","c");
$arr1 = array("a"=>1,"b"=>2,5,10=>100); //关联数组
$arr2 = array();
$arr2[] = "15";
$arr2[] = 15;
$arr3[] =100;
$arr3[] =10;
$arr3[] ='中国梦';
echo $arr3[0];

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If there are duplicate subscripts, the latter one will overwrite the previous one.

The order of the array units is determined by the order in which they are put in, not the subscripts

Array classification

Division by key-value relationship

Index array associative array mixed array

Divided by the dimensions of the array

One-dimensional array multi-dimensional array

Basic use of arrays

// 求一个一维数组的平均值 
$a = array(1,11,12,13,100);
$n =count($a);
$sum =0;
for ($i=0; $i <$n ; $i++) { 
		$sum+=$a[$i];
}
echo "一维数组的平均值是".$sum/$n."<br/>";
// 求一个二维数组的平均值
$a1 = array(
	array(10,11,100),
	array(10,101,100),
	array(100,300,100,400),
	);
$len = count($a1);
$sum = 0;
$c = 0;
for ($i=0; $i < $len; $i++) { 
	$tempconut = count($a1[$i]);
	for ($k=0; $k < $tempconut; $k++) { 
		$sum += $a1[$i][$k];
		$c++;
	}
}
echo "二维数组的平均值为".$sum/$c."<br/>";

// 求一个一维数组的最大值
$a3 = array(10,100,1,300);
$count = count($a3);
$max = $a3[0] ;
for ($i=0; $i < $count ; $i++) { 
	if($max < $a3[$i]){
		$max =  $a3[$i];
	}
}
echo "一维数组的最大值是".$max."<br>";
// 求一个二维数组的最大值
$a4 = array(
	array(100,0,10,999),
	array(100000000000000,100,10,9999),
	array(10,55,10000,999999999),
	);
$max = $a4[0][0];
for ($i=0; $i < count($a4); $i++) { 
	for ($k=0; $k < count($a4[$i]) ; $k++) { 
		if($max < $a4[$i][$k]){
			$max = $a4[$i][$k];
		}
	}
}
echo "二维数组的最大值是".$max."<br/>";
//交换一维数组的最大值和最小值
$arr5 = array(100,1,999,1024,888);
$max_index = -1;
$min_index = -1;
$max = $arr5[0];
$min = $arr5[0];
for ($i=0; $i < count($arr5); $i++) { 
	if($max < $arr5[$i]){
		 $max_index = $i;//最大值
		 $max = $arr5[$i];
	}
	
	if($min > $arr5[$i]){
		 $min_index = $i;//最小值
		 $min = $arr5[$i];
	}

}
$temp = $arr5[$max_index];
$arr5[$max_index] = $arr5[$min_index];
$arr5[$min_index] = $temp;
echo "最大值索引是".$max_index."最小值索引是".$min_index."<br/>";
echo "一维数组最大值和最小值交换后的结果为".implode(" ",$arr5)."<br>";

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Traversal of arrays<br/>

$arr = array(1,100,35);
foreach ($arr as $key => $value) {
	echo $value;
}

Array pointer operation

//数组指针操作
$arr = array(10,200,500);
do{
echo current($arr)."<br>";
}while(next($arr));
//指针默认在第一个元素处

$arr2 = array(100,88,1989,10,30);
foreach ($arr2 as $key => $value) {
	
}
$key = key($arr2);
$value = current($arr2);
//遍历之后指针的位置
var_dump($key); //NULL
var_dump($value); //false

for next traverse the array

$arr3 = array(1=>100,"aa"=>900,"中国梦");
for ($i=0; $i 
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while each() list() traverse the array

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