Which for loop correctly runs from i = 0 to i < n?

• A. for (int i = 1; i <= n; i++) { /* ... */ }
• B. for (int i = 0; i < n; i++) { /* ... */ }
• C. for (int i = 0; i <= n; i++) { /* ... */ }
• D. for (i = 0; i < n; i++) { /* ... */ }

Answer: (B)

The essential idea is to iterate exactly n times using indices that start at zero and stop before reaching n. A for loop that begins with i equal to 0 and continues while i is less than n achieves this, producing i values of 0, 1, 2, ..., n-1. That gives exactly n iterations with the index matching the common zero-based counting pattern.

Starting at 1 or going up to and including n changes the range, either skipping 0 or adding an extra iteration, so it no longer matches the required i = 0 to i < n sequence. Using i <= n while starting at 0 includes n as a value, resulting in one more iteration than intended. And omitting the type in the initialization would be a syntax error in languages that require an explicit declaration for the loop variable; the loop needs a properly declared i (for example, int i = 0).