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ccs50

C get every other digit from an int

I'm following CS50 course of Harvard University and I have to create a program in C that finds if a credit card number is valid or not. For example, I want from this number 378282246310005 to get the every other digit like this 7224300 so I started like this:

printf("Number\n");
long long cardNum = GetLongLong();

I don't know the methods I need to use to get the other digits to make my calculations.

Solution

  • Make use of simple division (/) and % operator to get this

    int number[20];
int count = 0;
long long cardNum = GetLongLong();
long long prevNum = cardNum;
while (cardNum < 10)
{
   cardNum = prevNum / 10;
   number[count] = prevNum % 10; 
   prevNum = cardNum;

   count++;
}