php的输出函数

echo "a","b","c";
echo ("a"),("b"),("c");
echo ("a","b","c");//错误
echo "a"."b"."c"

点号是将一个一个字符串连接起来，然后输出最终连接的结果

逗号是按顺序输出，没有字符串的拼接操作，所以速度快

echo是一个语言结构，不是一个函数，不能像给函数传参一样echo("a","b","c");

<?php
    print "acd"."sdf";
    print "acd","sdf";//错误
?>

echo能输出多个字符串，而print只能输出一个字符串

<?php
    print_r(23);//23
    print_r(array("a"=>1,"b"=>2));
?>

Array
(
    [a] => apple
    [b] => banana
    [c] => Array
        (
            [0] => x
            [1] => y
            [2] => z
        )

)

print_r(array("a"=>1,"b"=>2),true);//不输出结果，会将结果返回