Sendto not working Windows-Form Application

Question

I am working on socket programming(UDP sockets) in Windows-form application. I have called socket() on button click then I want send some bytes on other button click.Sendto() is returning 0 when I click the desired button but data is not received on the other end but when I call sendto() from a different thread within the same application it works fine.

Below is function to call socket():

int socket_create(String^* error,SOCKET *sock_fd,int port_number)
{
    sockaddr_in my_addr;
    *sock_fd = INVALID_SOCKET;

    // Create a SOCKET for the server to listen for client connections
    *sock_fd = socket(AF_INET, SOCK_DGRAM, 0);
    if (*sock_fd == INVALID_SOCKET)
    {
        this->richTextBox1->AppendText("Error at socket():"+     WSAGetLastError() + "\n");
        return -1;
    }
    else 
        this->richTextBox1->AppendText("Socket succesfully opened on port number: " + port_number + "\n");
    // The sockaddr_in structure specifies the address family,
    // IP address, and port for the socket that is being bound.
    my_addr.sin_family = AF_INET;
    my_addr.sin_addr.s_addr = inet_addr("192.168.1.2");
    my_addr.sin_port = htons(port_number);

    if (bind(*sock_fd, (SOCKADDR *) & my_addr, sizeof (my_addr)) == SOCKET_ERROR)
    {
        this->richTextBox1->AppendText("bind failed:" + WSAGetLastError()+ "\n");
        //freeaddrinfo(result);
        closesocket(*sock_fd);
        return -1;
    }
    else
        this->richTextBox1->AppendText("Bind succesful on port number:" + port_number + "\n");
    return 0;
}

Below is button code which calls socket_create() to open socket:

private: System::Void Connect_btn_Click(System::Object^  sender, System::EventArgs^  e) 
{
    int status = 0;
    String^ error;
    status = socket_create(&error, &s_8888,8888);   
}

socket descriptor s_8888 is defined globally.

Below is button code to call sendto():

private: System::Void test_btn_Click(System::Object^  sender, System::EventArgs^  e) 
{
    sockaddr_in their_addr;
    their_addr.sin_family = AF_INET;
    their_addr.sin_addr.s_addr = inet_addr(ip_address);
    their_addr.sin_port = htons(8888);
    int length = sizeof (their_addr);
    i=sendto(s_8888 , buf , sizeof(buf), 0, (SOCKADDR *) &their_addr, length);
    if(i== SOCKET_ERROR)
    {
        MessageBox::Show("" + WSAGetLastError());
    }
    richTextBox1->AppendText("" + i + "\n");
}

I am unable to understand why it is behaving like that and how to resolve it?