php字符串反转函数

Given a string and we have to reverse it without using a library function.

给定一个字符串，我们必须不使用库函数而将其反转。

Example:

例：

    Input: "Hello world!"
Output: "!dlrow olleH"
Input: "Welcome @ IncludeHelp.Com"
Output: "moC.pleHedulcnI @ emocleW"

PHP代码无需使用库函数即可反转字符串 (PHP code to reverse the string without using library function)

<?php
//PHP code to reverse the string without
//using library function
//function definition
//it accepts a string and returns the revrse string
function reverse_string($text){$rev = ''; //variable to store reverse string
$i = 0; //counting length
//calculating the length of the string
while(isset($text[$i])){$i++;
}
//accessing the element from the reverse
//and, assigning them to the $rev variable
for($j = $i - 1; $j >= 0; $j--){$rev .= $text[$j];
}
//returninig the reversed string
return $rev;
}
//main code i.e. function calling
$str = "Hello world!";
$r_str = reverse_string($str);
echo "string is: ". $str . "<br/>";
echo "reversed string is: ". $r_str . "<br/>";
$str = "Welcome @ IncludeHelp.Com";
$r_str = reverse_string($str);
echo "string is: ". $str . "<br/>";
echo "reversed string is: ". $r_str . "<br/>";
?>

Output

输出量

string is: Hello world!
reversed string is: !dlrow olleH
string is: Welcome @ IncludeHelp.Com
reversed string is: moC.pleHedulcnI @ emocleW

Explanation:

说明：

Since we can't use the library function, In the function - we run a for loop to reverse the strings by storing the sequence in reverse order in the variable $rev. An additional while loop is set up to check if the variable $text contains a valid string (i.e. to calculate the length). This is an additional safety check to ensure that the program works even if numbers are put into the function.

由于无法使用库函数，因此在函数中，我们运行一个for循环，以相反的顺序将序列存储在变量$ rev中，以反转字符串。 设置了一个附加的while循环，以检查变量$ text是否包含有效的字符串(即，计算长度)。 这是一项附加的安全检查，以确保即使在功能中输入了数字，程序也可以正常运行。

翻译自: https://www.includehelp.com/php/reverse-a-given-string-without-using-the-library-function.aspx

php字符串反转函数