title: Can't check return value of a function in C
body: <p>So I'm trying to check my functions return value in an if statement so that i can check wheter it's working fine or not.</p>
  
  <p>I have:</p>
  
  <pre><code>    if (int r = (input(num_first, num_second, fixPTR)) =! -1)
      {
  // do smth
      }
  </code></pre>
  
  <p>but Visual Studio says : expression must be a modifiable lvalue</p>
  
  <p>how do i fix it??</p>