title: How would I set up function to calculate the area of a circle - C
body: <p>I have this C program that needs to calculate the area of a circle that a user inputs.
  I have to use this before the main function:</p>
  
  <pre><code>void area_circum(double radius, double *area, double *circum);
  </code></pre>
  
  <p>I'm having trouble getting the program to work. I'm using the main function and another one called area_circum();</p>
  
  <p>This is what I have right now:</p>
  
  <pre><code>#include &lt;stdio.h&gt;
  
  
  void area_circum(double radius, double *area, double *circum);
  
  int main(void) {
  
      double radius, area, circum;
  
      printf("Please enter the radius of the circle: ");
      scanf("%f", &amp;radius);
  
      area_circum(radius, area, circum);
  
      printf("Area of circle : %0.4f\n", area);
  
      return 0;
  }
  
  
  void area_circum(double radius, double *area, double *circum) {
      double PIE = 3.141;
  
      double areaC = 0;
  
      areaC = PIE * radius * radius;
  }
  </code></pre>
  
  <p>When I build it and run it, it works, I input a number, but then it returns 0.00</p>