Loops: for and while

Why Loops?

Loops let you repeat code without writing it out multiple times. They're essential for counting, scanning, animations, and waiting.

The for Loop

Best when you know how many times to repeat:

for (int i = 0; i < 10; i++) {
  Serial.println(i);  // Prints 0-9
}

Structure: for (start; condition; step)

The while Loop

Best when you want to repeat until something changes:

while (digitalRead(buttonPin) == HIGH) {
  // Keep waiting until button is pressed
}
Serial.println("Button pressed!");

The do-while Loop

Runs at least once, then checks the condition:

do {
  // This runs at least once
  char key = keypad.getKey();
} while (key == NO_KEY);

Loop Patterns

Counting up

for (int i = 0; i <= 10; i++) { }

Counting down

for (int i = 10; i >= 0; i--) { }

Stepping by 2

for (int i = 0; i < 100; i += 2) { }

Looping through an array

int leds[] = {3, 5, 6, 9};
for (int i = 0; i < 4; i++) {
  digitalWrite(leds[i], HIGH);
}

Breaking Out

• break; exits the loop immediately
• continue; skips to the next iteration