C++函数重载

#include <iostream>
double add(double a, double b)
{
       return a + b;
}
int add(int a, int b)
{
       return a + b;
}
int add(int a, int b,int c)
{
       return a + b+c;
}
int main()
{
       const int num = 0;
       int a = 2;
       int b = 3;
       int d = 4;
       double e = 1.2;
       double f = 2.1;
       std::cout << add(e, f) << std::endl;
       return 0;
}