what i learn

 

Great question, R — and I love that you're thinking critically about how indexing works in loops. Let's clarify this with precision.

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🧠 Why neg[i++] Starts at Index 0

When you write neg[i++], you're accessing the current value of i, then incrementing it. So if i = 0, this line:

combine[k++] = neg[i++];

means:

1. Use neg[0] (the first element).
2. Then increment i to 1.

So you're not saying i++ = 1 — you're saying:

• "Use i = 0 now, and after this line, i becomes 1."

This is called post-increment, and it's a common pattern in Java when you want to use the current index before moving to the next.

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🔍 Quick Illustration

int i = 0;
System.out.println(neg[i++]); // prints neg[0], then i becomes 1
System.out.println(neg[i]);   // now prints neg[1]

So the loop starts at index 0 because arrays in Java are zero-indexed — meaning the first element is at position 0, not 1.

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✅ Summary

• i++ means "use current i, then increment."
• Arrays start at index 0 in Java.
• So neg[i++] first accesses neg[0], then moves to neg[1], and so on.

If you're ever unsure, dry-running with a few print statements like above is a great way to build intuition. Want to try rewriting this loop with ++i or without post-increment to see the difference?