PHP implements a method to convert a string into an integer (code example)

The content of this article is to introduce the method of converting a string into an integer in PHP (code example). It has certain reference value. Friends in need can refer to it. I hope it will be helpful to you.

Problem description
Convert a string to an integer (implement the function of Integer.valueOf(string), but return 0 when the string does not meet the numerical requirements), it is required that a library that cannot use strings to convert integers is required function. If the value is 0 or the string is not a legal value, 0 is returned.

Example 1:

Input: 2147483647
                                                                                                                                                                                                           

1. Processing negative signs

2. Processing positive signs

3. If the string contains non-numeric characters, 0 will be returned directly

4. '0' character The ascii code is 48

4. Traverse the string and start scanning from the 0 position. The current digital character ascii code minus the '0' character ascii code should be the integer at the current position

Algorithm:

StrToInt(str)
    if empty(str) return 0
    symbol=1
    if str[0]=='+' 
        symbol=1; str[0]='0'
    if str[0]=='-'
        symbol=-1; str[0]='0'
    res=0
    for i=0;i<str.size;i++
        if(str[i]<&#39;0&#39; || str[i]>'9') //包含非数字字符的，直接返回0
            res=0 break;
        res=res*10+str[i]-'0'  //进位用和ascii相减算出整型数字
    res=symbol*res //加上正负号
    return res

php implementation (code example):

<?php
function StrToInt($str){
        if (empty($str)){return 0;} 
        $symbol=1;
        if ($str{0}==&#39;+&#39;){ 
                $symbol=1; 
                $str{0}=&#39;0&#39;;
        }   
        if ($str[0]==&#39;-&#39;){
                $symbol=-1; 
                $str{0}=&#39;0&#39;;
        }   
        $res=0;
        for ($i=0;$i<strlen($str);$i++){
                if($str{$i}<&#39;0&#39; || $str{$i}>'9'){ //包含非数字字符的，直接返回0
                        $res=0;
                        break;
                }   
                $res=$res*10+$str{$i}-'0'; //进位用和ascii相减算出整型数字
        }   
        $res=$symbol*$res; //加上正负号
        return $res;
}
$s="-123";
$res=StrToInt($s);
var_dump($res);

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