Bind failed: Address already in use

I am attempting to bind a socket to a port below:

if( bind(socket_desc,(struct sockaddr *) &server, sizeof(server)) < 0)
{
    perror("bind failed. Error");
    return 1;
}
puts("bind done");

But it gives:

$ ./serve   
Socket created    
bind failed. Error: Address already in use

Why does this error occur?