# Credit card checkpoint algorithm the luhn mod-10

Source: Internet
Author: User

Nothing to say, just make a backup ~

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According to the Payment Card checkpoint in ISO 2894AlgorithmThe luhn mod-10 method rules:

1. Multiply each digit on the card number by the weight. The rule is that if the number of card numbers is an even number, the first digit is multiplied by 2; otherwise, the number is multiplied by 1, and then the numbers are, 1, 2, 1, 2;
2. If each digit is multiplied by 9 after the weight, 9 is subtracted;
3. sum all processed weighted numbers and calculate the modulus using number 10;
4. The remainder should be 0, otherwise it may be an input error. It may also be a fake number.

With the simple implementation of PHP, front-end verification is better in actual scenarios, such as Js.

`Function check_card (\$ card) {If (! Is_numeric (\$ card) return false; \$ card_len = strlen (\$ card); \$ I = 0; \$ num_ I = array (); do {If (! \$ I) {\$ num_x = \$ card_len % 2? 1: 2;} else {\$ num_x = 1? 2: 1;} \$ num_ I [\$ I] = (INT) \$ card [\$ I] * \$ num_x; \$ num_ I [\$ I] = \$ num_ I [\$ I]> 9? \$ Num_ I [\$ I]-9: \$ num_ I [\$ I];} while (isset (\$ card [++ \$ I]); \$ num_sum = array_sum (\$ num_ I); return \$ num_sum % 10? False: true ;}`

PS: What should I do if I have a preliminary interview question ~

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