title: invalid type argument of unary '*'
body: <p>I'm a week into an intro programming class, and I'm having trouble with fixing what's supposed to be a relatively simple code. I keep getting an invalid type argument of unary '*' error. </p>
  
  <pre><code>#include &lt;stdio.h&gt;
  #define PI 3.14159; 
  int main()
  {
     float r;
     float area;
     scanf("%f", &amp;r);
     area = PI * r * r;
     printf("Area is %f", area);
     return 0; 
  }
  </code></pre>
  
  <p>Could someone explain this, and how to fix it? </p>