php地图数字到字符串

I am trying to write a program in php which first prompts a user for a string. once they enter a string it is supposed to give the equivalent digits if it were on a phone. eg ABC(2) , DEF(3) , GHI(4) , JKL(5) , MNO(6) , PQRS(7) , TUV(8) , WXYZ(9). Im using a for loop and nested if statements but i am not getting the correct output. Am I going about this the right way? my code is below

<?php

$str = $_POST['usersString'];

$len = strlen($str);

for($i=0; $i<$len-1; $i++){
    if($i="a" || $i="b" || $i="c"){
        echo "1";
    }

    if($i="d" || $i="e" || $i="f"){
        echo "2";
    }

    if($i="g" || $i="h" || $i="i"){
        echo "3";
    }
}    

?>
<form action="task17.php" method="POST">
Enter a string <input type="text" name="usersString" />
<input type="submit" value="enter" />
</form> 

<?php

$str = $_POST['usersString'];

$len = strlen($str);

for($i=0; $i<$len; $i++){

   if($str[$i]=="a" || $str[$i]=="b" || $str[$i]=="c"){
    echo "1";

   }else if($str[$i]=="d" || $str[$i]=="e" || $str[$i]=="f"){
    echo "2";

   }else if($str[$i]=="g" || $str[$i]=="h" || $str[$i]=="i"){
    echo "3";
   }
}    

?>

your condition is wrong $i="a" It should be $str[$i]=="a"

$i isn't going to be a letter in your loop, it's going to be an integer. What you want is to use $i as the offset of $str like $str[$i]. So with 'abc' $str[0] will be 'a'.

I would personally use an array for this to store the values:

$len = strlen($str);
$array = [ 'a' => 1, 'b' => 1, 'c' => 1, 'd' => 2, 'e' => 2, 'f' => 2 ];
// and so on...

for($i=0; $i<$len; $i++){
  echo $array[ $str[$i] ];
}

Note that I also used $i<$len rather than $i<$len-1. I don't think you want to use less than with -1. This would lead you to exclude the last character.

1. Use $str[$i] instead of $i in your If conditions like

   if($str[$i]=="a" || $str[$i]=="b" || $str[$i]=="c"){ echo "1"; }

2. change your for loop to

   for($i=0; $i < $len; $i++)
   {   
   }
   

$str = "ADFJ";
$digitArr = array('abc', 'def', 'ghi', 'jkl', 'mno', 'pqrs', 'tuv', 'wxyz');
$strlne= strlen($str);
$digCount = count($digitArr);
for ($i = 0; $i < $strlne; $i++) {
    $j = 0;
    while ($j < $digCount) {
        if (stripos($digitArr[$j], $str[$i]) !== false) {
            $output[] = $j+1;
            break;
        }
        $j++;
    }
}
print_r($output);