negative number help!

[idgaf12]

My code runs, but for some reason my average is coming back with a negative number...

#include <cstdlib> 
#include <iostream> 
using namespace std; 

int main() 
{ 
double score[5] = {0.0,0.0,0.0,0.0,0.0};
double lowest = 0.0; 
double highest = 0.0; 
double avg = 0.0;
double sum = 0.0;

for (int i = 0.0; i<5; i = i + 1) 
{ 
	score[i] = 0.0; 
} 

cout << "You will be asked to enter 5 scores."<< endl; 
for (int i = 0.0; i<5; i = i + 1) 
{ 
cout << "Please enter a score: "; 
cin >> score[i]; 
} 
lowest = score[0];
for (int i=1; i<5; i=i+1)
{
	if (score[i] < lowest)
	{
		lowest = score [i];	
	}
}
highest = score[0];
for (int i=1; i<5; i=i+1)
{
	if (score[i] > highest)
	{
		highest = score[i];
	}
} 
for (int i=1; i<5; i=i+1)
{
	avg = sum + score[i] - lowest - highest;
}

cout << "Lowest Score: " <<lowest<<endl;
cout << "Highest Score: " <<highest<<endl;
cout << "Average score with highest score and lowest score excluded: " <<avg<<endl;

system("pause"); 
	return 0;
}