Whats the problem in this code? last 2 test case didn't match

Question

https://code.sololearn.com/cxtu19OQcJI4/?ref=app

Below is the problem :

You need to verify if the given credit card number is valid. For that you need to use the Luhn test.

Here is the Luhn formula:
1. Reverse the number.
2. Multiple every second digit by 2.
3. Subtract 9 from all numbers higher than 9.
4. Add all the digits together.
5. Modulo 10 of that sum should be equal to 0.

Task:
Given a credit card number, validate that it is valid using the Luhn test. Also, all valid cards must have exactly 16 digits.

Input Format:
A string containing the credit card number you need to verify.

Output Format:
A string: 'valid' in case the input is a valid credit card number (passes the Luhn test and is 16 digits long), or 'not valid', if it's not.

Sample Input:
4091131560563988

Sample Output:
valid

Update : Solved by just adding if (n == 16) condition. and nested the whole process into it.
else will be printed "not valid"

Answer 1

Yes, thanks, I'm reading...

Answer 2

You could copy...

Answer 3

I'm a bit confused of the middle-part, the second loop. Can't test it, but I would at least shorten it a bit:
for (i = 0; i < n; i + 2) {
num[i] = (str[i] * 2);

if ( num[i] > 9){
num[i]-=9;
}

Answer 4

Thanks All 😊
Just solve it by just doing if (n != 16) the condition going execute not valid.

just a little fix

Answer 5

This is a Pro-code coach, so you'll have better chances for help, if you would at least post the description.

Answer 6

Sandra Meyer I've to manually write the problem?

Answer 7

Sandra Meyer Now Is it okay?

Answer 8

Martin Taylor oh, i just need to filter it with the 0-9 condition?
like if (str[i] >= '0' && str[i] <= '9')

Answer 9

Martin Taylor I used gets because fgets gives me 1 length more

Answer 10

Martin Taylor Still (after filtering by isdigit and 0-9 also) Number 6, 7 test case failed like earlier.
* 6 & 7 case are locked. so, I am unable to find the bug

Answer 11

Hey Jubaer Ahmad,
I Am Posting My Code Here Based On Luhn’s Algorithm To Validate A Credit Card:
https://code.sololearn.com/cIo1IRS8tYRM/?ref=app
My Code Passed All The Test Cases So With The Help Of This Code You May Find Some Help.
✌️✌️