Getting an undefined reference error

[rcpomasl]

NOTE: THIS IS HOMEWORK. PLEASE POINT ME IN THE RIGHT DIRECTION - DO NOT JUST GIVE ME THE ANSWER. THANK YOU!

Here's my code: main.cpp (https://gist.github.com/rcpomasl/72bf819b95d46477b1dc), stddev.cpp (https://gist.github.com/rcpomasl/a8ac167b47e784e713ee), stddev.hpp (https://gist.github.com/rcpomasl/189df1517fc53bb17478). I'm including links rather than just posting my code here because I'm not sure where the error is, so I would need to post all of my code, which would probably take more space than is available.

Here's what the shell is giving me:

main.cpp: (.text + 0x190): undefined reference to 'stddev::computeAverage(std::string)'
main.cpp: (.text + 0x2a9): undefined reference to 'stddev::computeStdDev(std::string)'

I'm fairly new to C++. Do I need to do something additional to call functions that belong to another class? Have I made "Java" assumptions? Anything you can do to help will be appreciated. The lines that are calling those functions are lines 34 and 44.

[helios]

The functions in stddev.cpp are global functions, not member functions. It'd be better to get rid of the class stddev, since it doesn't contain any data.

[rcpomasl]

Could you give me a quick explanation on the difference between global and member functions? I'm inclined to keep stddev, if only because I will be reusing the code throughout the semester.

[helios]

Why would you be unable to reuse the code if stddev wasn't there?

class Foo
    //Member function
    void bar();
};

//Global function
void bar();

//Member function
void Foo::bar(){
}

//Global function
void bar(){
}

[rcpomasl]

I would still be able to - I'm calling that my last resort if I can't get this figured out. I just want to have the code in it's own little package, rather than integrated into my main.

Based on advice from other people, I've added stddev:: to the functions in stddev.cpp, but this hasn't solved the problem.

[helios]

I just want to have the code in it's own little package, rather than integrated into my main.

You don't need classes for that.

[rcpomasl]

Well, I solved it. I needed to change the <> around the .hpp file include statement to " ".

[JLBorges]

> I just want to have the code in it's own little package
Use a namespace, perhaps?
http://www.cplusplus.com/doc/oldtutorial/namespaces/

Header stddev.hpp

#include <string>

namespace stddev // stat_utils would be a better name
{
    double computeAverage( std::string sequence ) ;
    // ...
}

Implementation stddev.cpp

// #include <stddev.h>
#include "stddev.h" // use "" for your own headers
#include <sstream>

double stddev::computeAverage( std::string sequence )
{
    int sum = 0 ;
    std::istringstream numbers(sequence);
    int currentNum = 0;

    // this construct is canonical in C++
    while( numbers >> currentNum ) // for each number read from the stream
    {
        // validate range
        // ...
        // if valid, add to sum
    }
    return sum ;
}

// ... 

main.cpp

#include "stddev.h" 

// ...

int main()
{
    std::string current_line ;

    // ...

    auto avg = stddev::computeAverage(current_line) ;

    // ...
}

// ...