Why Loops Exist

Imagine debugging the name of every account in this List, one at a time:

List<String> accountNames = new List<String>{'Acme Corp', 'Globex', 'Initech', 'Umbrella Corp', 'Soylent Co'};

System.debug(accountNames[0]);
System.debug(accountNames[1]);
System.debug(accountNames[2]);
System.debug(accountNames[3]);
System.debug(accountNames[4]);

1. List<String> accountNames = new List<String>{...}; — five accounts.
2. (blank line) 3-7. System.debug(accountNames[0]); through System.debug(accountNames[4]); — one hand-written line per item, by index.

This works for 5. It's unworkable for 500, and it breaks the moment the list's size changes. A loop replaces all of this with one block of code that runs once per item, however many items there are.

List<String> trackingNumbers = new List<String>{'TRK001', 'TRK002', 'TRK003'};

for (String trackingNumber : trackingNumbers) {
    System.debug('Checking status for ' + trackingNumber);
}

1. List<String> trackingNumbers = new List<String>{...}; — three tracking numbers.
2. (blank line)
3. for (String trackingNumber : trackingNumbers) { — a loop (covered fully starting next lesson) that runs once per item in the List, automatically.
4. System.debug('Checking status for ' + trackingNumber); — runs once for each tracking number in turn.
5. } — closes the loop.

A logistics batch job doesn't know in advance how many shipments it needs to check — it could be 3 or 30,000. A loop handles both identically, which is exactly the point.

Apex gives you several loop shapes for different situations: for, the enhanced for, while, and do-while, plus break/continue for controlling a loop mid-run. The final lesson covers governor limits — the hard ceiling Salesforce places on how much looping code can do, and why it matters more here than almost anywhere else in Apex.