Putting code in Multiple Files.

• This is a topic covered in chapter 12, but I want it now.
  • It starts on page 610
• In order to go to the next step of programming we need to learn how to put our code in different files.
  • This allows for the development of reusable code
  • And for multiple people to work on a project at the same time.
  • And allows us to implement test drivers.
  • And it allows us to focus on a small portion of our code.
• We will probably see this code again, but let's focus on making a set of routines that will allow us to deal with numbers in base 3.
• A little design first.
  • I can store numbers in an int.
  • And by default I can get the base 10 representation out of that.
  • But other bases require more work.
  • In this case, I will need a way to read in and output base 3 numbers.
  • So I will store them in a string.
• What are the digits for base 3 numbers {0,1,2}
• How do I covert from base 3 to base 10
  • 120₃ = ? base 10
  • Just use the rule you know

    $1 x 3^2 + 2 x 3^1 + 0 x 3^0 = 1x9 + 2x3 + 0x0 = 9+6+0 = 15$
    

• Can I convert from base 10 to base 3?
  • Once again, you should have learned the algorithm in 123.
  • Just continue to mod and div by 3.
  • Lets try 462.

      3|462
       +---
      3|154  R 0
       +---
       3|51  R 1
        +--
       3|17  R 0
        +--
        3|5  R 2
         +-
          1  R 2
              

  • Reading the remainders backwards we get 122010₃
• So a reasonable set of functions would be
  • string IntToTrinary(int number)
  • int TrinaryToInt (string number)
• So in the past we would have done something like

  #include <iostream>
  #include < string>
  
  using namespace std;
  
  string IntToTrinary(int number);
  int TrinaryToInt(string number);
  
  ...
  
  int main() {
  }
  
  string IntToTrinary(int number){
  }
  
  int TrinaryToInt(string number){
  } 

• But this means, we had the functions tied to our main routine.
  • If we wanted to use them in another program in the future, we had to copy the code.
  • If we wanted to test the routines, this had to be built into our main program.
• Neither of these situations are good.
• The solution is isolating these functions in their own files.
• In general, I like to place related routines, and their constants, in a set of files.
• We will do that next.