CS50 Credit Problem is skipping "else if" part - c

Question

I am really stuck here. The programm gives right answer to invald credit card numbers but never say if its VISA, AMEX or MASTERCARD.
I need to post the complete code because I do not have so much experience wit the C language.
The checksum part in the end could also have been "bool" but I always got error messages with that.
#include <cs50.h>
#include <stdio.h>
int main(void)
{
long long card;
int checksum = 0;
do
{
card = get_long_long("Number: ");
}while (card <= 0);
int count = 0;
while (card != 0) {
card /= 10; // n = n/10
++count;
}
if(count != 16 && count != 13 && count != 15){
printf("INVALID\n");
}
else if(checksum != 0){
printf("INVALID\n");
}
else if(card >= 34e13 || card >= 37e13){
printf("AMEX\n");
}
else if(card >= 51e14 || card >= 52e14 || card >= 53e14 || card >= 54e14 || card >= 55e15) {
printf("MASTERCARD\n");
}
else if(card >= 4e15 || card >=4e12) {
printf("VISA\n");
}
else {
printf("INVALID\n");
}
}
int checksum(long long card_nr)
{
int sum = 0;
for (int i=0;card_nr !=0; i++, card_nr/=10 )
{
if(i % 2 == 0)
sum += card_nr % 10;
else
{
int digit = 2 * (card_nr % 10);
sum += digit / 10 + digit % 10;
}
}
return (sum % 10) == 0;
}
There may be major issue or only some parenthesis, the programm is compiling. Thanks for any help.

Answer 1

There are many errors with the logic:
#include <cs50.h>
#include <stdio.h>
int main(void)
{
long long card;
int checksum = 0;
do
{
card = get_long_long("Number: ");
}while (card <= 0);
int count = 0;
// ** In here you destroy card, so later card whill allways be 0
while (card != 0) {
card /= 10; // n = n/10
++count;
}
if(count != 16 && count != 13 && count != 15){
printf("INVALID\n");
}
else if(checksum != 0){
printf("INVALID\n");
}
//** here it is the same as if(card >= 34e13)
else if(card >= 34e13 || card >= 37e13){
printf("AMEX\n");
}
//** here it is the same as if(card >= 51e14)
//** also these values are already covered by last check
else if(card >= 51e14 || card >= 52e14 || card >= 53e14 || card >= 54e14 || card >= 55e15) {
printf("MASTERCARD\n");
}
//** here it is the same as if(card >= 4e15)
//** also these values are already covered by previous check
else if(card >= 4e15 || card >=4e12) {
printf("VISA\n");
}
else {
printf("INVALID\n");
}
}
int checksum(long long card_nr)
{
int sum = 0;
for (int i=0;card_nr !=0; i++, card_nr/=10 )
{
if(i % 2 == 0)
sum += card_nr % 10;
else
{
int digit = 2 * (card_nr % 10);
sum += digit / 10 + digit % 10;
}
}
return (sum % 10) == 0;
}```

Answer 2

After loop:
while (card != 0) {
card /= 10; // n = n/10
++count;
}
card = 0 and original card number is lost.
You can save original card number to another variable and then compare it.
Also it is better to use integer constants like 54LL << 14 instead of float 54e14