for Loops

A loop with a counter built in

• A for loop 计数循环 packs three parts into one line:
• for (int i = 0; i < 5; i++) { ... }
• Initialization (int i = 0), condition (i < 5), update (i++).
• Use for when you know how many times to repeat.

The three parts, in order

• Initialization runs once, before the loop starts.
• The condition is checked before each pass (like while).
• The update runs after each pass, then the condition is re-checked.
• So the flow is: init → (test → body → update) → (test → body → update) → …

The three parts of a for loop and the order they run

for and while are interchangeable

• Any for loop can be rewritten as a while loop, and vice versa.
• for (int i=0; i<5; i++) {B} equals int i=0; while (i<5) {B; i++;}.
• for is tidier when the counter setup, test, and change belong together.
• Choose whichever makes the loop's intent clearest.

Counting a known number of times

• for (int i = 0; i < n; i++) runs the body exactly n times (i = 0 to n-1).
• Change the bounds to count differently: i = 1; i <= n runs n times too.
• Watch the boundary: < stops one before, <= includes the end.
• This is the standard pattern for "do something n times."