break, continue, and Loop Guards

break and continue

• break — leave the loop NOW (innermost one only).
• continue — skip to the next iteration.

for (int i = 0; i < 10; i++) {
    if (i % 2 == 0) continue;   // skip evens
    if (i > 7) break;           // stop after 7
    printf("%d ", i);           // 1 3 5 7
}

Off-by-one

The classic: <= vs < with a 0-based index.

int a[5] = {1, 2, 3, 4, 5};
for (int i = 0; i <= 5; i++) printf("%d ", a[i]);   // BUG: a[5] is out of bounds
for (int i = 0; i < 5; i++)  printf("%d ", a[i]);   // correct

Out-of-bounds access is undefined behavior — the module 9 rule is born here: the last valid index is size - 1.

The runaway condition

If the update step moves AWAY from the exit condition (for (int i = 0; i < 5; i--)), or nothing in the body changes the tested variable, the loop never ends. When a loop misbehaves, print the loop variable each pass and watch.