The way I understand it.. in simplest terms... When you compile this code.. it "sees" you declared those functions... now when you call upon it it "jumps" to the function.

I myself do it the other way...

Code:
#include <iostream>
using namespace std;

int WidthInFeet()
{
  ///blah blah
}

int WidthInInches(int feet)
{
  return feet * 12;
}

int main()
{
  int feet = WidthInFeet();
  int wd   = WidthInInches(feet);

  cout << wd;
 
  return 0;
}