user36986: I am creating a home weather station but the Arduino IDE shows 
"expected ';' before 'viewport'". 

It detects wrong quotation marks. My code:
     String message2 = "<!DOCTYPE html>";
  message2 += "<head>";
  message2 +=  "<title>Bootstrap Example</title>";
  message2 += " <meta name="viewport" content="width=device-width, initial-scale=1">";
  message2 += "<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css">";
  message2 +=  "<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script>";
  message2 +=  "<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/js/bootstrap.min.js"></script>";
  message2 += "</head>";
  message2 += "<body>";
  message2 += "<div class="container">";
  message2 +=  "<h2>Teplotná Stanica</h2>";
  message2 +=  "<p>Teplota:";
  message2 +=  dht.readTemperature();
  message2 +=  "</p>";

  server.send(200, "text/html", message2);}

Can someone tell me what´s wrong?
I am using Arduino IDE

user31105: In C you can not use quotation marks inside quotation marks (thus nested).
Replace 
message2 += " <meta name="viewport" content="width=device-width, initial-scale=1">";

to
message2 += " <meta name=\"viewport\" content=\"width=device-width, initial-scale=1\">";

By using the escape character \  it means that \" is a character (")  instead of the beginning or start of a string.

36986: <p>I am creating a home weather station but the Arduino IDE shows </p>

<pre><code>"expected ';' before 'viewport'". 
</code></pre>

<p>It detects wrong quotation marks. My code:</p>

<pre><code>     String message2 = "&lt;!DOCTYPE html&gt;";
  message2 += "&lt;head&gt;";
  message2 +=  "&lt;title&gt;Bootstrap Example&lt;/title&gt;";
  message2 += " &lt;meta name="viewport" content="width=device-width, initial-scale=1"&gt;";
  message2 += "&lt;link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css"&gt;";
  message2 +=  "&lt;script src="https://ajax.googleapis.com/ajax/libs/jquery/3.2.1/jquery.min.js"&gt;&lt;/script&gt;";
  message2 +=  "&lt;script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/js/bootstrap.min.js"&gt;&lt;/script&gt;";
  message2 += "&lt;/head&gt;";
  message2 += "&lt;body&gt;";
  message2 += "&lt;div class="container"&gt;";
  message2 +=  "&lt;h2&gt;Teplotná Stanica&lt;/h2&gt;";
  message2 +=  "&lt;p&gt;Teplota:";
  message2 +=  dht.readTemperature();
  message2 +=  "&lt;/p&gt;";

  server.send(200, "text/html", message2);}
</code></pre>

<p>Can someone tell me what´s wrong?
I am using Arduino IDE</p>
 31105: <p>In C you can not use quotation marks inside quotation marks (thus nested).</p>

<p>Replace </p>

<pre><code>message2 += " &lt;meta name="viewport" content="width=device-width, initial-scale=1"&gt;";
</code></pre>

<p>to</p>

<pre><code>message2 += " &lt;meta name=\"viewport\" content=\"width=device-width, initial-scale=1\"&gt;";
</code></pre>

<p>By using the escape character \  it means that \" is a character (")  instead of the beginning or start of a string.</p>
