Your code should not include unnamed numerical constants also known as "magic numbers" or "magic constants". For example, there is one in this code to shuffle a deck of cards:
# Bad code for (int i = 0; i < 52; i++) { const int j = i + rand() % (52-i); swap(cards[i], cards[j]); }
This code is bad because the meaning of 52 is not explained and it is arbitrary. A better code would be:
const int deck_size = 52; for (int i = 0; i < deck_size; i++) { int j = i + rand() % (deck_size - i); swap(cards[i], cards[j]); }