[c++] Include header files

// primer.h
#include <string> // V headerju includamo samo <string>, in ne tudi <cmath>, ker bom ta file vključil v primer.cpp

double power(double base, double exponent);
std::string upperCase(const std::string& str);

//---------------------------------------------------------------
// primer.cpp
#include <cmath>

double power(double base, double exponent)
{
    return pow(base, exponent);
}

std::string upperCase(const std::string& str)
{
    // ....
}