无法在php中显示运算符

I am trying to make a math game where two numbers are generated and are either added or subtracted from each other every time u type the answer. i can get the numbers to display but i cant get the operator to display. how would i do that? here is my code:

php

<?php

$num1 = rand(0, 20);
$num2 = rand(0, 20);

$operators = array(
    "+",
    "-",  
);

switch ($operators[array_rand($operators)]) {
    case "+":
        $result = $num1 + $num2;
        break;
    case "-":
        $result = $num1 - $num2;
        break;
}
    echo'
        <div class="row">                   
            <div class="col-md-3 col-md-offset-1">'. $num1 .'</div>
            <div class="col-md-3 col-md-offset-1">'. $operators .'</div>
            <div class="col-md-3 col-md-offset-1">'. $num2 .'</div>

        </div>        
        '
?>

<?php

$num1 = rand(0, 20);
$num2 = rand(0, 20);

$operators = array(
    "+",
    "-",  
);
$operator = $operators[array_rand($operators)];
switch ($operator) {
    case "+":
        $result = $num1 + $num2;
        break;
    case "-":
        $result = $num1 - $num2;
        break;
}
    echo'
        <div class="row">                   
            <div class="col-md-3 col-md-offset-1">'. $num1 .'</div>
            <div class="col-md-3 col-md-offset-1">'. $operator .'</div>
            <div class="col-md-3 col-md-offset-1">'. $num2 .'</div>

        </div>        
        '
?>

try to somethinf like this...

<?php

$num1 = rand(0, 20);
$num2 = rand(0, 20);

$operators = array("+","-",
);
$operator =  $operators[array_rand($operators)];
switch ($operator) {
    case "+":
        $result = $num1 + $num2;
        break;
    case "-":
        $result = $num1 - $num2;
        break;
}
    echo'
        <div class="row">
            <div class="col-md-3 col-md-offset-1">'. $num1 .'</div>
            <div class="col-md-3 col-md-offset-1">'. $operator.'</div>
            <div class="col-md-3 col-md-offset-1">'. $num2 .'</div>

        </div>
        '
?>

<?php

$num1 = rand(0, 20);
$num2 = rand(0, 20);

$operators = array(
    "+",
    "-",  
);



switch ($operator=$operators[array_rand($operators)]) {
    case "+":
        $result = $num1 + $num2;
        break;
    case "-":
        $result = $num1 - $num2;
        break;
}
    echo'
        <div class="row">                   
            <div class="col-md-3 col-md-offset-1">'. $num1 .'</div>
            <div class="col-md-3 col-md-offset-1">'. $operator .'</div>
            <div class="col-md-3 col-md-offset-1">'. $num2 .'</div>


        </div>        
        '
?>