I need help in understanding how the functions works in the program inorder to identify the lowest value in the array

[Dave Jones]

#include <iostream>
#include <iomanip>
using std::cout;
using std::endl;
using std::setw;

double& lowest(double values[], const int& length); // Function prototype

int main(void)
{
double data[] = { 3.0, 10.0, 1.5, 15.0, 2.7, 23.0,4.5, 12.0, 6.8, 13.5, 2.1, 14.0 };

int len(_countof(data)); // Number of elements

for(auto value : data)
cout << setw(6) << value;

lowest(data, len) = 6.9; // Change lowest to 6.9
lowest(data, len) = 7.9; // Change lowest to 7.9
cout << endl;

for(auto value : data)
cout << setw(6) << value;
cout << endl;
return 0;
}
// Function returning a reference
double& lowest(double a[], const int& len)
{
int j(0); // Index of lowest element
for(int i = 1; i < len; i++)
if(a[j] > a[i]) // Test for a lower value...
j = i; // ...if so update j
return a[j]; // Return reference to lowest element
}


*I need help in understanding how the function works in this program. I am confuse in how the for loop works in the function that indicates the lowest value in the array. Thanks in advance