# Answer to Question #43047 in C++ for nona

Question #43047

2. Compute the sum of single digit numbers obtained from step 1 above:

Sum of even single-digits = 4 + 4 + 8 + 2 + 3 + 1 + 7 + 8 = 37

3. Compute the sum of every odd digit from right to left:

Sum of odd digits = 6 + 6 + 0 + 8 + 0 + 7 + 8 + 3 = 38

4. Compute the sum of the results from step 2 and step 3:

Total sum = 37 + 38 = 75

5. If the total sum from step 4 is divisible by 10, the card number is valid. Otherwise

itâ€™s not valid.

Is 75 divisible by 10 (without remainder)? No, the card number in this

example is Invalid.

Sum of even single-digits = 4 + 4 + 8 + 2 + 3 + 1 + 7 + 8 = 37

3. Compute the sum of every odd digit from right to left:

Sum of odd digits = 6 + 6 + 0 + 8 + 0 + 7 + 8 + 3 = 38

4. Compute the sum of the results from step 2 and step 3:

Total sum = 37 + 38 = 75

5. If the total sum from step 4 is divisible by 10, the card number is valid. Otherwise

itâ€™s not valid.

Is 75 divisible by 10 (without remainder)? No, the card number in this

example is Invalid.

Expert's answer

`#include<iostream>`

#include<string>

**using** **namespace**std**;**

intmain**()** **{**

cout **<<** "Enterthe card number: "**;**

string cardNumber**;**

cin **>>**cardNumber**;**

bool valid **=** **true****;**

int sumOfOdd **=** 0**;**

int sumOfEven **=** 0**;**

// The credit card number muststart with 3, 4, 5 or 6.

**if** **((**cardNumber**[**0**]** **!=** '3'**)** **&&** **(**cardNumber**[**0**]** **!=** '4'**)** **&&** **(**cardNumber**[**0**]** **!=** '5'**)** **&&** **(**cardNumber**[**0**]** **!=** '6'**))** **{**

valid **=** **false****;**

**}**

// The total number of digits ofa credit card number must be between 13 to 16 digits.

**if** **((**cardNumber**.**length**()** **<** 13**)** **||** **(**cardNumber**.**length**()** **>** 16**))** **{**

valid **=** **false****;**

**}**

// Luhn Rule

**for** **(**int i **=** 0**;** i **<**cardNumber**.**length**();** i**++)** **{**

char c **=**cardNumber**[**cardNumber**.**length**()** **-** i **-** 1**];**

intnum **=** c **-** '0'**;**

**if** **((**num**<** 0**)** **||** **(**num**>** 9**))** **{**

valid **=** **false****;**

**}**

**if** **(**i **%** 2 **==** 1**)** **{**

num **=** 2 *****num**;**

**if** **(**num**>** 9**)** **{**

num **=**num **/** 10 **+**num **%** 10**;**

**}**

sumOfEven **=**sumOfEven **+** num**;**

**}**

**else** **{**

sumOfOdd **=**sumOfOdd **+** num**;**

**}**

**}**

int sum **=**sumOfOdd **+** sumOfEven**;**

**if** **(**sum**%** 10 **!=** 0**)** **{**

valid **=** **false****;**

**}**

**if** **(**valid**)** **{**

cout **<<** "Thecard is valid" **<<** endl**;**

**}**

**else** **{**

cout **<<** "Thecard is invalid" **<<** endl**;**

**}**

**return** 0**;**

**}**

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