sum of 2 numbers in cpp

#include<iostream>
int add(int,int);
int main()
{
	using namespace std;
	int a,b;
	cout<<"Enter first number: ";
	cin>>a;
	cout<<"Enter second number: ";
	cin>>b;
	cout<<"Sum = "<<add(a,b);
}
int add(int x,int y)
{
	return(x+y);
}

#include<iostream>
using namespace std;
int main()
{
	double number1,number2;
  	double sum0;
  	sum=number1+number2;
  	cout<<sum;
}