title: Check if user input is digit
body: <p>I got this code that is supposed to check if user input is a digit or not but it prints "false" no matter if it's a digit or not.</p>
  
  <pre><code>if (isdigit(atoi(argv[1])))
  {
     printf("true");
  }
  else
  {
     print("false");
  }
  </code></pre>
  
  <p>This is how i run it:</p>
  
  <p>./filename 2 3</p>