PHP 制作了一个计算器，出了点问题，求解！

这是我做0输入的处理代码：

===============================================================

if($_POST['num0']){
    $num=$_POST['num0'];
   if(is_dir('txt')){
            $open=fopen("txt/caculator.txt","r+");
            if(is_file("txt/caculator.txt")){
                $a=file_get_contents("txt/caculator.txt");
                $e=(int)$a;
                $b=$e."0";
                echo $b;
                file_put_contents("txt/caculator.txt",$b); 
                fclose($open);
            }
           }
                }
=================================================================
这是表单：
=================================================================

=================================================================
全部代码在二楼。
主要意思就是 先在localhost下创建文件夹txt，再在文件夹txt下创建文件caculator.txt
caculator2.txt; caculator3.txt; 单击对应数字将数字显示到文本框，并存储到caculator.txt，
然后单击运算符，将对应运算符存储到caculator3.txt中，并将caculator.txt中的字符串存入caculator2.txt，然后清空caculator.txt，这是单击数字按钮输入第二个运算数字，并将第二个运算
数字存入caculator.txt中，当单击等于号，先对caculator3.txt中存入的运算符进行判断，然后进行
相应的运算。
其他都没问题，都可以实现，问题出现在输入0的时候，程序不会把0存入到文件中，导致0的输入不能实现，
不知道什么问题，求解答。初步估计是数据类型的问题。。。

回复讨论(解决方案)

if(is_dir('txt')){         if(is_file("txt/caculator.txt")){             if(is_readable("txt/caculator.txt")){                 echo file_get_contents("txt/caculator.txt");             }         }        }else {         echo "0";        } ?>"/>

if(!is_dir('txt')){
    if(!is_file("txt/caculator.txt")){
 echo"<script>alert('请在localhost下创建文件夹txt，并在文件夹txt下创建3个文件，分别是caculator.txt <br /> caculator2.txt caculator3.txt 然后才能正常完成任务！');</script>";
  }}
if($_POST['num0']){
    $num=$_POST['num0'];
   if(is_dir('txt')){
            $open=fopen("txt/caculator.txt","r+");
            if(is_file("txt/caculator.txt")){
                $a=file_get_contents("txt/caculator.txt");
                $e=(int)$a;
                $b=$e."0";
                echo $b;
                file_put_contents("txt/caculator.txt",$b); 
                fclose($open);
            }
           }
                }
//单击数字1的反应
        if($_POST['num1']){
    $num=$_POST['num1'];
   if(is_dir('txt')){
            $open=fopen("txt/caculator.txt","r+");
            if(is_file("txt/caculator.txt")){
                $a=file_get_contents("txt/caculator.txt");
                $b=$a.$num;
                file_put_contents("txt/caculator.txt",$b); 
                fclose($open);
            }
           }
                }
                
                if($_POST['num2']){
 //单击数字2的反应   
    $num2=$_POST['num2'];
     if(is_dir('txt')){
            if(is_file("txt/caculator.txt")){
                $open=fopen("txt/caculator.txt","r+");
                $open;
                $a=file_get_contents("txt/caculator.txt");
                $b=$a.$num2;
                file_put_contents("txt/caculator.txt",$b); 
                fclose($open);
            }
           }
               }
//单击数字3的反应
 if($_POST['num3']){
    
    $num=$_POST['num3'];
     if(is_dir('txt')){
            if(is_file("txt/caculator.txt")){
                $open=fopen("txt/caculator.txt","r+");
                $open;
                $a=file_get_contents("txt/caculator.txt");
                $b=$a.$num;
                file_put_contents("txt/caculator.txt",$b); 
                fclose($open);
            }
           }
               }
//单击数字4的反应
 if($_POST['num4']){
    
    $num=$_POST['num4'];
     if(is_dir('txt')){
            if(is_file("txt/caculator.txt")){
                $open=fopen("txt/caculator.txt","r+");
                $open;
                $a=file_get_contents("txt/caculator.txt");
                $b=$a.$num;
                file_put_contents("txt/caculator.txt",$b); 
                fclose($open);
            }
           }
               }
//单击数字5的反应
 if($_POST['num5']){
    
    $num=$_POST['num5'];
     if(is_dir('txt')){
            if(is_file("txt/caculator.txt")){
                $open=fopen("txt/caculator.txt","r+");
                $open;
                $a=file_get_contents("txt/caculator.txt");
                $b=$a.$num;
                file_put_contents("txt/caculator.txt",$b); 
                fclose($open);
            }
           }
               }
//单击数字6的反应
 if($_POST['num6']){
    
    $num=$_POST['num6'];
     if(is_dir('txt')){
            if(is_file("txt/caculator.txt")){
                $open=fopen("txt/caculator.txt","r+");
                $open;
                $a=file_get_contents("txt/caculator.txt");
                $b=$a.$num;
                file_put_contents("txt/caculator.txt",$b); 
                fclose($open);
            }
           }
               }
//单击数字7的反应
 if($_POST['num7']){
    
    $num=$_POST['num7'];
     if(is_dir('txt')){
            if(is_file("txt/caculator.txt")){
                $open=fopen("txt/caculator.txt","r+");
                $open;
                $a=file_get_contents("txt/caculator.txt");
                $b=$a.$num;
                file_put_contents("txt/caculator.txt",$b); 
                fclose($open);
            }
           }
               }
//单击数字8的反应
 if($_POST['num8']){
    
    $num=$_POST['num8'];
     if(is_dir('txt')){
            if(is_file("txt/caculator.txt")){
                $open=fopen("txt/caculator.txt","r+");
                $open;
                $a=file_get_contents("txt/caculator.txt");
                $b=$a.$num;
                file_put_contents("txt/caculator.txt",$b); 
                fclose($open);
            }
           }
               }
//单击数字9的反应  
 if($_POST['num9']){
    
    $num=$_POST['num9'];
     if(is_dir('txt')){
            if(is_file("txt/caculator.txt")){
                $open=fopen("txt/caculator.txt","r+");
                $open;
                $a=file_get_contents("txt/caculator.txt");
                $b=$a.$num;
                file_put_contents("txt/caculator.txt",$b); 
                fclose($open);
            }
           }
               }  
               //单击 点 的反应
                if($_POST['dot']){
        
    $num=$_POST['dot'];
    
    if(is_dir('txt')){
            if(is_file("txt/caculator.txt")){
                $open=fopen("txt/caculator.txt","r+");
                $open;
                $a=file_get_contents("txt/caculator.txt");
                $findme= ".";
                $pos=strpos($a, $findme);
                if($pos==true){
                 
                      file_put_contents("txt/caculator.txt",$a); 
                        fclose($open); 
                }
                else{
                    $b=$a.$num;
                    file_put_contents("txt/caculator.txt",$b); 
                    fclose($open);
                    }
            }
           }
               }   
//单击选项C的反应
 if($_POST['Clear']){
    
    
     if(is_dir('txt')){
            if(is_file("txt/caculator.txt")){
                $open=fopen("txt/caculator.txt","w+");
                $open;
                $open=fopen("txt/caculator2.txt","w+");
                $open2;
                $open=fopen("txt/caculator3.txt","w+");
                $open3;
               
            }
           }
               }  
                //单击 ← 的反应  
if($_POST['back']){
        if(is_dir('txt')){
            if(is_file("txt/caculator.txt")){
                $open=fopen("txt/caculator.txt","r+");
                $open;
                $a=file_get_contents("txt/caculator.txt");
                $a=substr($a,0,-1);
               file_put_contents("txt/caculator.txt",$a);
            }
           }
               }   
//单击+的反应
       if($_POST['add']){
        if(is_dir('txt')){
           if(is_file("txt/caculator2.txt")&&is_file("txt/caculator.txt")&&is_file("txt/caculator3.txt")){
                $open=fopen("txt/caculator.txt","r+");
                $open;
                $open2=fopen("txt/caculator2.txt","r+");
                $open2;
                $open3=fopen("txt/caculator3.txt","r+");
                $open3;
                $b="";
                $c="+";
                $a=file_get_contents("txt/caculator.txt");
                file_put_contents("txt/caculator.txt",$b);
                file_put_contents("txt/caculator2.txt",$a);
                file_put_contents("txt/caculator3.txt",$c);
            }
           }
        
       }  
//单击-的反应
 if($_POST['sub']){
        if(is_dir('txt')){
           if(is_file("txt/caculator2.txt")&&is_file("txt/caculator.txt")&&is_file("txt/caculator3.txt")){
                $open=fopen("txt/caculator.txt","r+");
                $open;
                $open2=fopen("txt/caculator2.txt","r+");
                $open2;
                $open3=fopen("txt/caculator3.txt","r+");
                $open3;
                $b="";
                $c="-";
                $a=file_get_contents("txt/caculator.txt");
                file_put_contents("txt/caculator.txt",$b);
                file_put_contents("txt/caculator2.txt",$a);
                file_put_contents("txt/caculator3.txt",$c);
            }
           }
        
       } 
 //单击乘的反应
  if($_POST['mul']){
        if(is_dir('txt')){
           if(is_file("txt/caculator2.txt")&&is_file("txt/caculator.txt")&&is_file("txt/caculator3.txt")){
                $open=fopen("txt/caculator.txt","r+");
                $open;
                $open2=fopen("txt/caculator2.txt","r+");
                $open2;
                $open3=fopen("txt/caculator3.txt","r+");
                $open3;
                $b="";
                $c="*";
                $a=file_get_contents("txt/caculator.txt");
                file_put_contents("txt/caculator.txt",$b);
                file_put_contents("txt/caculator2.txt",$a);
                file_put_contents("txt/caculator3.txt",$c);
            }
           }
        
       } 
          //单击=的反应 
       if($_POST['equal']){
        if(is_dir('txt')){
           if(is_file("txt/caculator2.txt")&&is_file("txt/caculator.txt")&&is_file("txt/caculator3.txt")){
                $open=fopen("txt/caculator.txt","r+");
                $open;
                $open2=fopen("txt/caculator2.txt","r+");
                $open2;
                $open3=fopen("txt/caculator3.txt","r+");
                $open3;
                $a=file_get_contents("txt/caculator.txt");
                $b=file_get_contents("txt/caculator2.txt");
                $c=file_get_contents("txt/caculator3.txt");
                $nul="";
                if($c=="+"){
                    $d=$b+$a;
                }
                if($c=="-"){
                    $d=$b-$a;
                }
                if($c=="*"){
                    $d=$a*$b;
                }
                if($c=="/"){
                    $d=$b/$a;
                }
                if($c=="%"){
                    $d=$b%$a;
                }
                if($c=="+"){
                    $d=$a+$b;
                }
                if($c=="√"){
                    $d=sqrt($a);
                }
                file_put_contents("txt/caculator.txt",$d);
                
            }
           }
        
       }     

以上是大部分代码，由于输入字符有限，关键代码贴出来了。

好多代码 你还是 直接说哪里出问题了吧  说关键的

你的问题在于：
if($_POST['num0']){
因为 $_POST['num0'] 等于 0，所以条件恒不成立。该分支不会进入！
应改作
if($_POST['num0'] == '0'){

你的程序设计的很不合理，需要做大幅度调整
文件操作函数的使用也欠妥
既然是用 file_get_contents、file_put_contents 读写文件，那么就不需要 fopen、fclose 再来做摆设了
file_put_contents 有一个 FILE_APPEND 参数可以附加内容到文件，而无需读出后人工追加

如果需要，可以你一个调整后的代码供参考

用AJAX，然后动态PHP编译就得了，实际把一大堆公司放进去计算好了。

你的问题在于：
if($_POST['num0']){
因为 $_POST['num0'] 等于 0，所以条件恒不成立。该分支不会进入！
应改作
if($_POST['num0'] == '0'){

你的程序设计的很不合理，需要做大幅度调整
文件操作函数的使用也欠妥
既然是用 file_get_contents、file_put_contents 读写文件，那么就不需要 fope……
版主大神啊...我还是刚开始学的...
求以后多多指教！