With a debit card, you deposit money first and then spend it. Like a credit card, you can swipe the card at the POS machine to spend. With a credit card, you can spend first and repay later. Therefore, a debit card only has some functions of a credit card and cannot be used completely as a credit card.

If you use your credit card as a debit card and deposit it first and then spend it, you will be losing money. Using a credit card for overdraft consumption and then repaying it within the interest-free period allows you to use the bank's money without having to pay interest; conversely, by first depositing a lot of money on your credit card and then slowly spending on the card, not only does it not account for the overdraft "Cheap", and no interest is paid on the money stored there, which actually gives the bank an advantage.