To Comment or Not to Comment

Comments are not always helpful.

Bad

// Subtract discount from final price.
final_price = (num_items * item_price) -
              std::min(5, num_items) * item_price *  0.1;

// Filter offensive words.
for (std::string word : words) { ... }

int width = ...; // Width in pixels.

// Safe since height is always > 0.
return width / height;

It's often better to make your code self-explanatory.

Good

price = num_items * item_price;
discount = std::min(5, num_items) * item_price * 0.1;
final_price = price - discount;

FilterOffensiveWords(words);

Pixels width = ...;

CheckArgument(height > 0);
return width / height;

Avoid using comments to explain what code does. Use comments to explain why code does something.