credit cs50 solution
#include <stdio.h>
#include<cs50.h>
#include <math.h>
int main(void)
{
long x = get_long("enter the credit card number");
int digit = 0, sum = 0;
//digit is used for odd and even checker.
long y = x;
//checksum card digits
while (y != 0)
{
int sumeven = 0, sumodd = 0;
int rem = y % 10;
digit++;
if (digit % 2 == 0) //if digit is even
{
int multiply = rem * 2;
if (multiply == 0)
{
sumeven += multiply;
}
else
{
while (multiply != 0) //adding all digits after
{
sumeven += multiply % 10;
multiply /= 10; //minus last digit of multiply
}
}
}
else //if digit is odd
{
sumodd += rem;
}
y /= 10; //minus last digit from y
sum += sumeven + sumodd;
}
//check for valid credit card
if (digit != 13 && digit != 15 && digit != 16) //for first if
{
printf("INVALID\n");
}
else if (sum % 10 == 0)
{
if (digit == 16) //if digit is 16
{
if (x / 100000000000000 >= 51 && x / 100000000000000 <= 55)
{
printf("MASTERCARD\n");
}
else if (x / 1000000000000000 == 4)
{
printf("VISA\n");
}
else //if digit is not 16
{
printf("INVALID\n");
}
}
else if (digit == 15)
{
if (x / 10000000000000 == 34 || x / 10000000000000 == 37)
{
printf("AMEX\n");
}
else
{
printf("INVALID\n");
}
}
else if (digit == 13)
{
if (x / 1000000000000 == 4)
{
printf("VISA\n");
}
else
{
printf("INVALID\n");
}
}
}
else
{
printf("INVALID\n");
}
}`