Welding-Torch · July 21, 2023 16:49 · Jul 21, 2023 · Jul 21, 2023
diff --git a/credit.c b/credit.c
@@ -1 +1,146 @@
-‎‎
+#include <cs50.h>
+#include <stdio.h>
+
+int initialvalidate(long cardnumber); // Checks if cardnumber is 13, 15, or 16 digits long.
+int validate(long cardnumber); // Luhn's algorithm.
+string whichbrand(long cardnumber); // Tells which brand i.e. VISA, MASTERCARD, AMEX.
+int countdigits(long num); // Used for initial validation.
+
+int main(void)
+{
+    int valid, initialvalidation;
+    string brand;
+    long cardnumber = get_long("Number: ");
+    initialvalidation = initialvalidate(cardnumber);
+    if (initialvalidation == 1)
+    {
+        valid = validate(cardnumber); // should be 0 or 1
+        if (valid == 1)
+        {
+            brand = whichbrand(cardnumber);
+            printf("%s", brand);
+        }
+        else
+        {
+            printf("INVALID\n");
+        }
+    }
+    else
+    {
+        printf("INVALID\n");
+    }
+}
+
+int countdigits(long num)
+{
+    int count = 0;
+    do
+    {
+        count++;
+        num = num / 10;
+    }
+    while (num != 0);
+
+    return count;
+}
+
+int initialvalidate(long cardnumber) // check if cardnumber is less than 13 or more than 16
+{
+    if (countdigits(cardnumber) < 13)
+    {
+        return 0;
+    }
+    else if (countdigits(cardnumber) == 13)
+    {
+        return 1;
+    }
+    else if (countdigits(cardnumber) == 14)
+    {
+        return 0;
+    }
+    else if (countdigits(cardnumber) == 15)
+    {
+        return 1;
+    }
+    else if (countdigits(cardnumber) == 16)
+    {
+        return 1;
+    }
+    else
+    {
+        return 0;
+    }
+}
+
+int validate(long cardnumber) // Luhn’s Algorithm
+{
+    int sum = 0, othersum = 0, counter = 1, total = 0, currentnum, currentnumtimes2;
+    long restofcardno;
+    restofcardno = cardnumber;
+
+    do
+    {
+        currentnum = restofcardno % 10;
+        if (counter % 2 == 0) // if it is even, do this
+        {
+            currentnumtimes2 = currentnum * 2;
+            if (currentnumtimes2 > 9)
+            {
+                sum = sum + currentnumtimes2 / 10 + currentnumtimes2 % 10;
+            }
+            else
+            {
+                sum = sum + currentnumtimes2;
+            }
+        }
+        else // if it is odd, do this.
+        {
+            othersum = othersum + currentnum;
+        }
+        counter++;
+        restofcardno = restofcardno / 10;
+    }
+    while (restofcardno != 0);
+
+    total = sum + othersum;
+    if (total % 10 == 0)
+    {
+        return 1;
+    }
+    else
+    {
+        return 0;
+    }
+}
+
+int getFirst2Digits(long input)
+{
+    while (input >= 100)
+    {
+        input /= 10;
+    }
+
+    return input;
+}
+
+string whichbrand(long cardnumber)
+{
+    int First2 = getFirst2Digits(cardnumber);
+    if (First2 == 34 || First2 == 37)
+    {
+        return "AMEX\n";
+    }
+    else if (First2 == 51 || First2 == 52 || First2 == 53 || First2 == 54 || First2 == 55)
+    {
+        return "MASTERCARD\n";
+    }
+    else if (First2 / 10 == 4)
+    {
+        return "VISA\n";
+    }
+    else
+    {
+        return "INVALID\n";
+    }
+
+}
diff --git a/credit.c b/credit.c
@@ -0,0 +1 @@
+‎‎