function - Error Message: undefined reference to 'printHeader()' & undefined reference to 'calculateArea(double&)' -

i wrote program calculate area of circle , keeps giving me error message: "undefined reference 'printheader() , undefined reference 'calculatearea(double&)'"

i cannot figure out means! i've looked everywhere including site of answers way above head.

program:

#include <iostream> using namespace std;  // aquire radius value // postcondition: print out header , return radius value double printheader();  // precondition: radius has been entered // postcondition: calculate , print out area of circle void calculatearea(double& radius);  int main() {     double area=0.0, radius=0.0;     printheader();     calculatearea(radius);     return 0; }  double printheader(double& radius) {     cout << "program calculating area of circle" << endl;     cout << "enter radius of circle: ";     cin >> radius;     return radius; }  void calculatearea(double& radius, double area) {     double pi=3.14159;     area = (pi*radius*radius);     cout << "the area of circle is: " << area << endl; } 

i using codeblocks. much!

this error compiler telling you have declared functions have not been defined. if @ function prototypes:

// aquire radius value // postcondition: print out header , return radius value double printheader();  // precondition: radius has been entered // postcondition: calculate , print out area of circle void calculatearea(double& radius); 

then @ functions define later:

double printheader(double& radius) { ... }  void calculatearea(double& radius, double area) { ... } 

you can see not defining functions have prototypes - number of parameters different! compiler identifies functions based on scope , parameters. need update forward declarations include parameters in definitions:

double printheader(double& radius); void calculatearea(double& radius, double area); 

another way of describing function double printheader() not same function double printheader(double& radius) - first takes no parameters , second requires double reference.