title: C++ error: warning: multi-character character constant/atof usage
body: <p>C++ newbie.  Could someone please explain to me what error messages I received mean or why am I getting them?  Thank you.  </p>
  
  <pre><code>#include &lt;iostream&gt;
  #include &lt;string&gt;                                                                                                                            
  
  int main () {
     std::string input;
     double f, k;
  
     /* edit: codes to go inside the do while loop */                                                                                                                                   
     std::cout &lt;&lt; "\nEnter Fahrenheit temperature or 'exit' to end program: "; 
     std::getline(std::cin, input);
  
     do {
       f = std::atof(input.c_str());  //convert string input to double
       k = (f + 459.67) * (5/9);
       std::cout &lt;&lt; "Entered Fahrenheit temperature is: " &lt;&lt; f &lt;&lt; std::endl;                                                                         
       std::cout &lt;&lt; "Temperature in Kelvin is " &lt;&lt; k &lt;&lt; std::endl &lt;&lt; std::endl;
  
     }while(input != 'exit');  //program runs until input is 'exit'
  
     return 0;
  }
  
  Errors:
  t.cc:21:19: warning: multi-character character constant
  t.cc: In function `int main()':
  t.cc:21: error: no match for 'operator!=' in 'input != 1702390132'
  </code></pre>
  
  <p>EDIT:
  Thank you everyone for the advice on while(input != 'exit').  Could someone check that I'm using atof correctly in the calculation section?  I'm not getting any calculation with what I have. If I enter 45, I get k = 0 instead or 250.   </p>