Is the uint "ID" in this function saved in storage?

Question

I am a bit confused about the uint "id" in the start function.

I understand that the uint "nextCampaignId" is a global variable, and so changes made to it will be saved in storage; which means that with each new campaign created, "nextCampaignId" will be incremented, and so cannot be used to determine ID numbers of previously created campaigns. Hence, we need to assign its value to a new uint "id" within the function.

However, I thought integers declared within functions do not get saved in storage. Wouldn't this ID number be lost once the function is terminated? Does the function simply return the ID (to the UI) and then forgets it? But then how can we retrieve specific campaign data later?

uint nextCampaignId;
mapping(uint256 => CampaignData) campaigns;

// Start a new campaign.
function start(address recipient, uint256 goal, uint256 deadline) returns 
(uint id) {
    var campaign = campaigns[nextCampaignId];
    campaign.recipient = recipient;
    campaign.goal = goal;
    campaign.deadline = deadline;
    nextCampaignId ++;
    id = nextCampaignId;
}

Answer 1

Almost everything you say is true, but nextCampaignId isn't declared inside the function. It's just used inside the function.

If it was declared there, the function would look something like this:

function start(address recipient, uint256 goal, uint256 deadline) returns 
(uint id) {
    var campaign = campaigns[nextCampaignId];
    campaign.recipient = recipient;
    campaign.goal = goal;
    campaign.deadline = deadline;
    uint nextCampaignId;
    nextCampaignId ++;
    id = nextCampaignId;
}

Also, the reason why id = nextCampaignId; is needed is just because the function header says that the variable id should be returned. Nothing else. It could also be a simple return nextCampaignId;.