New to C++

[slimg00dy]

Hey guys, I'm new to C++, I'm reading the C++ primer book, sixth edition, and in chapter 2, listing 2.6, there is a sample code to convert pounds to stones. Essentially it just takes the input from the user in stones and multiply that by 14 which returns the total number of pounds.

I wanted to modify this and return the number of stones from the number of pounds input by the user. However I ran into a snag when the return for most reverse conversion ended up in floating point numbers. So I changed the instantiated prototype of the function that does divides the input by 14 to a floating type function, as well as the function itself on the body.

I have searched the web to see if there are a ways to return floating point numbers however I feel that I do not understand C++ well enough to see how they work exactly, perhaps someone here can show how to return floating point numbers from the second function in my case and I may understand from there (hopefully).

Here is code below. I prefer doing everything on github so all of the corrections, are in one area if you don't mind, otherwise, I'll keep a watch on my e-mail.

Thanks in advanced. Again I'm completely new to C++ and most programming languages, so please be detailed as possible as it will help me out :)

The original code from the book.  
// convert.cpp -- converts stone to pounds
#include <iostream>
int stonetolb(int);     // function prototype
int main()
{
using namespace std;
int stone;
cout << "Enter the weight in stone: ";
cin >> stone;
int pounds = stonetolb(stone);
cout << stone << " stone = ";
cout << pounds << " pounds." << endl;
return 0;
}
int stonetolb(int sts)
{
return 14 * sts;
}

Modified code to return stones to pounds:
https://github.com/slimg00dy/LearningC/blob/master/ch2-StoneToPounds.cpp 

[LB]

slimg00dy on GitHub wrote:

 float lbtostone(int pds)
 {
  return pds / 14;
 }

The issue is that you need to divide by 14.0f instead of 14, otherwise you will have integer division followed by conversion to float.

By the way, unless you have a need to use float, use the double type instead (and 14.0 instead of 14.0f).

[slimg00dy]

Hello LB,

Thank you for that detailed output. I've made the changes to double, when instantiating and declaring the function, I've also made the change to 14.0.

I understand that double is supposed to give me double precision, in laymen's terms, more numbers after the fractional point (eg. 1.589548954893282).

After making the changes and compiling the source, I still get the same output.

Also, how did you do that "Code on Github wrote:"

Thanks again in advanced.

// Convert.cpp -- converts stones to pounds
#include <iostream>
double lbtostone(int); // function prototype instantiated
int main()
{
  int pounds;
  std::cout << "Enter the weight in pounds: ";
  std::cin >> pounds;
  int stone = lbtostone(pounds);
  std::cout << pounds << " pounds = ";
  std::cout << stone << " stone." << std::endl;
  return 0;
}

double lbtostone(int pds)
{
 return pds / 14.0;
}

./ch2-StoneToPounds
Enter the weight in pounds: 156
156 pounds = 11 stone.

[LB]

On line 9 you take the double precision float and store it into an integer, truncating the decimal places.

As for the quote, it is like on most forums: [quote=name of person]text[/quote]

[slimg00dy]

Hello again LB,

Thank you for catching that, you're right, I was passing stone as an "int" rather than a "double"

I have another question, do I need to instantiate my lbtostone function as "double"

[LB]

slimg00dy wrote:

I have another question, do I need to instantiate my lbtostone function as "double"

I don't understand your question; functions cannot be instantiated.

[slimg00dy]

Hi,

I was referring to the function prototype. It does look like the "double" is required in the prototype.