Data error in dynamic object array in arduino

Currently I'm using Arduino for my project and what I want is to have an array that stores an array of sensors. I do understand that there's limited resource to be used for a dynamic array. But by limiting the number of items in the array and uses struct data instead of creating a class, I managed to cut the SRAM cost. So without further ado, here's my code :

#define MAX_SENSOR 6

namespace Sensors
{
    typedef struct
    {
        byte SlavePin;
        byte LDRPin;
        byte RedPin;
        byte BluePin;
    } Sensor;

    Sensor _sensors[MAX_SENSOR];
    byte _len = 0;

    void Add(Sensor s)
    {
        if (_len > MAX_SENSOR)
            return;
        _len++;
        _sensors[_len] = s;
    }

    Sensor Get(byte index)
    {
        return _sensors[index];
    }
}

And here's how I use it.

#include "Sensors.h"

void setup()
{
    for (int i = 0; i < 6; i++)
    {
        Sensors::Sensor sen;
        sen.SlavePin = 0;
        Sensors::Add(sen);
    }
    Serial.print("Length = ");
    Serial.println(Sensors::_len);

    for (int j = 0; j < Sensors::_len; j++)
    {
        Serial.print(j);
        Serial.print(" = ");
        Serial.println(Sensors::Get(i).SlavePin);
    }
}

void loop() { //Nothing goes here }

This code works and it compiles successfully. But when I run it, the serial window shows this :

Length : 6

Sensor 0:0

Sensor 1:0

Sensor 2:1

Sensor 3:2

Sensor 4:3

Sensor 5:4

Apparently, the first and the second item in the array has the same value and honestly, I don't know why.

Here's the output that I'm expecting :

Length : 6

Sensor 0:0

Sensor 1:1

Sensor 2:2

Sensor 3:3

Sensor 4:4

Sensor 5:5

Any help would be very appreciated. And BTW, I'm sorry if this kind of thread had already existed.