Stuck on Challenge Task - Functional Programming in C

I'm stumped on this one ...

Write a function named "addTwo" that accepts two float numbers as arguments. The function should also return a float which is the sum of the two arguments passed to the function.

Here's the code I wrote ...

float addTwo(float a, float b);
int main() 
{

    float one = 2.5;
  float two = 10.5;

  float sum = addTwo(one, two);
  printf("The sum of one and two is %f\n", sum);

  return 0;

}

float addTwo(float a, float b) {
            return a+b;

 }

When I run this in Xcode it works fine, but the challenge screen comes back with this when I preview it ...

conflicting types for 'main' int main(int argc, const char * argv[]) ^ note: previous definition is here int main() ^ 1 error generated.

I have had trouble in the past understanding some of the questions because half the time I don't know how much of the actual code is required to satisfy the question. My understanding is that the source code will always include an int main() function block.

Any guidance would be greatly appreciated ... Scott