I ran into a situation where I needed to create user account programmatically in Drupal 7. Here is simple process to do this:
//This will generate a random password, you could set your own here
$password = user_password(8);
//set up the user fields
$fields = array(
'name' => 'user_name',
'mail' => '[email protected]',
'pass' => $password,
'status' => 1,
'init' => 'email address',
'roles' => array(
DRUPAL_AUTHENTICATED_RID => 'authenticated user',
//the first parameter is left blank so a new user is created
$account = user_save('', $fields);
// If you want to send the welcome email, use the following code
// Manually set the password so it appears in the e-mail.
$account->password = $fields['pass'];
// Send the e-mail through the user module.
drupal_mail('user', 'register_no_approval_required', $email, NULL, array('account' => $account), variable_get('site_mail', '[email protected]'));
Note: You can add additional roles inside the role array using the role id as the array index and the role name as the value.