# When I multiply my array by 2 it doesn't give expected value

Also, please when I try to add "firstnumsum", it doesn't give expected value and I don't know what to do.

#include <cs50.h> #include <stdio.h> #include <string.h> #include <stdlib.h>

bool checksum(string checksumarray[0]);

int main() { long long cardnumber = 0, calc; //string credit[1]; //string lengthkey[1]; string credit; string lengthkey[1];

``````//user input
do
{
credit = get_string("Card number: ");
}
while ((credit <= 0));
//to check if condition works
printf("%s credit\n", credit);

//the long long version of user's string input
cardnumber = strtoll(credit, NULL, 10);

//copy of long long for calculation
calc = cardnumber;

string checksumarray[1];
checksumarray[0]= credit;
//luhn's algorithm
bool checksum(string checksumarray[0]);
{
long long /*lastdigit, reverse = 0,*/ mult, remaining, firstnumsum = 0, easier, sum_of_even = 0,  finalsum;
int /*countcardcharacters = 0,*/ a = strlen(checksumarray[0]);
//sum the odd digits
for (int x = a - 1; x >= 0; x -= 2)
{
easier = strtoll (checksumarray[0][x], NULL, 10);
printf("%lli checksumarray\n",easier);
firstnumsum = firstnumsum + easier;
}
printf("%lli firstsum\n", firstnumsum);
//sum of even digits
for (int j = a - 2; j >= 0; j -=2)
{
printf("%c checksumarray2\n", checksumarray[0][j]);
mult = checksumarray[0][j];
mult *= 2;
//mult = (checksumarray[0][j]) * 2;
printf("%lli mult\n", mult);
do
{
remainder = mult % 10;
mult -= remainder;

printf("%lli remainder\n", remainder);
sum_of_even += remainder;
mult /= 10;
printf("%lli sum of even\n", sum_of_even);
}
while (!(mult > 0));

}
finalsum = firstnumsum + sum_of_even;
printf("%lli final\n", finalsum);
if (finalsum % 10 == 0)
return true;
else
return false;
}

``````

## 1 Answer

this converts it from its ASCII form

``````    (checksumarray[0][x] - '0')
``````