Linking two .cpp and a .h files

Question

I'm doing an exercise (from the third chapter of Thinking in C++) but I have a problem linking two .cpp files.

This is the exercise:

Create a header file (with an extension of ‘.h’). In this file, declare a group of functions by varying the argument lists and return values from among the following: void, char, int, and float. Now create a .cpp file that includes your header file and creates definitions for all of these functions. Each definition should simply print out the function name, argument list, and return type so you know it’s been called. Create a second .cpp file that includes your header file and defines int main( ), containing calls to all of your functions. Compile and run your program.

I've created the three files, but when I try to compile the compiler give me this error:

undefined reference to `func1()'

undefined reference to `func2(int)'|

undefined reference to `func3(char, int, double)'|

undefined reference to `func4()'|

||=== Build finished: 4 errors, 0 warnings ===|

Why it cannot found the function declaration?

##EDIT
These are my three files:

func_ex.h

void func1(void);
int func2(int i);
char func3(char c, int i, double d);
float func4(void);

func_ex.cpp

#include "func_ex.h"
using namespace std;

void func1(void) {
    cout << "void func1(void)" << endl;
}

int func2(int i) {
    cout << "int func2(int i)" << endl;
}

char func3(char c, int i, double d) {
    cout << "func3(char c, int i, double d)" << endl;
}

float func4(void) {
    cout << "func4(void)" << endl;
}

func_ex_main.cpp

#include "func_ex.h"
#include <iostream>
using namespace std;

int main(int argc, char* argv[]) {
    func1();
    int i;
    func2(i);
    char c; double d;
    func3(c, i, d);
    func4();
}

I'm usig GCC as compiler (and Code::Blocks as IDE, but I think that's not important).

Answer 1

It sounds like the file is not finding the functions appropriately. Is the header file included in both files? You can include it like:

#include "myheader.h"

Did you make sure to compile both files together? Such as:

gcc -o myprogram file1.cpp file2.cpp