# problem at the output of credit (pset1)

i have problem with Credit (pset1), my problem is not about the algorithm but about something wired , the output of subtract and multiplication is not right at all
first of all i get a valid input from the user and store it in long double variable.then, then i got another 2 long double variables , one will be equal to input subtracted by 100 , and the other will be equal to the second variable but after applying truncl() function to it to get rid of decimal number.then, i subtract 2nd and 3rd variables to get the last 2 digits and multiply it by 100 to be able to have those 2 digits outside of number like this.

``````    long double creditNumber;
long double checker1, checker2;
do
{
creditNumber = get_long_long("Enter Your Credit card number: ");
}while(!creditNumber);
while(creditNumber / 100 >= 10)
{
checker1 = creditNumber / 100;  //divide input by 100 to separate last 2 digits
printf("%Lf\n", checker1);
checker2 = truncl(checker1);     //convert number after division to decimal
printf("%Lf\n", checker2);
checker3 = (checker1 - checker2) * 100; //subtract both number to get just last 2 digits
printf("%f\n", checker3);
x = checker3 ;             //double 2 digits by 100 and assignt it to integerif(checker3 < 10)
``````

my problem that , suppose that the input is 5555555555554444 so first of all checker1 = 55555555555544.44 but this doesnt happen, the output of checker 1 is 55555555555544.439999 and that's ruined my whole code because every number i try to check will be decreased by one, so how to solve this . and this is my whole code if you have any comment or correction on my algorithm.

``````#include <cs50.h>
#include <stdio.h>
#include <math.h>

int main(void)
{
int x,y,z = 0;
int counter = 0;
int numberChecker = 0;
float checker3;
long double creditNumber;
long double checker1, checker2;
do
{
creditNumber = get_long_long("Enter Your Credit card number: ");
}while(!creditNumber);
while(creditNumber / 100 >= 10)
{
checker1 = creditNumber / 100;  //divide input by 100 to separate last 2 digits
printf("%Lf\n", checker1);
checker2 = truncl(checker1);     //convert number after division to decimal
printf("%Lf\n", checker2);
checker3 = (checker1 - checker2) * 100; //subtract both number to get just last 2 digits
printf("%f\n", checker3);
x = checker3 ;             //double 2 digits by 100 and assignt it to integerif(checker3 < 10)
printf("%i\n", x);
if(x < 10)
{
numberChecker += x;
printf("%i\n", numberChecker);
}
else
{
y = x % 10 ;                    //that will get just last digit
printf("%i\n", y);
z = x / 10 ;                    //that will get second to last digit
printf("%i\n", z);
numberChecker += (z*2) + y;     //the mathematic operation needed to check validation
//by double second to last digit and add it to last digit.
printf("%i\n", numberChecker);
}
counter += 2;                   //counting how many digits have been eliminated
printf("%i\n", counter);
creditNumber = creditNumber / 100;
printf("%Lf\n", creditNumber);
}
if(creditNumber < 100)
{
if(counter != 14)
{
printf("INVALID\n");
}
else
{
x = creditNumber;
y = x % 10;
z = creditNumber / 10;
numberChecker += (z*2) + y;
if(numberChecker % 10 != 0)
{
printf("Invalid\n");
}
else
{
if(creditNumber == 51 || creditNumber == 52 || creditNumber == 53 || creditNumber == 54 ||
creditNumber == 55 )
{
printf("MASTERCARD\n");
}
else
{
x = creditNumber / 10 ;
if (x == 4)
{
printf("VISA\n");
}
else
{
printf("Invalid\n");
}
}
}
}
}
else if(creditNumber > 100)
{
if(counter == 10)
{
x = creditNumber;
y = x % 10;
numberChecker += y;
x = x / 10;
y = x % 10;
numberChecker += (y*2);
x = x / 10;
numberChecker += x;
if(numberChecker % 10 != 0)
{
printf("INVALId\n");
}
else
{
if(x == 4)
{
printf("VISA\n");
}
else
{
printf("INVALiD\n");
}
}
}
else if(counter == 12)
{
x = creditNumber;
y = x % 10;
numberChecker += y;
x = x / 10;
y = x % 10;
numberChecker += (y*2);
x = x / 10;
numberChecker += x;
if(numberChecker % 10 != 0)
{
printf("INVAlID\n");
}
else
{
if(x == 34 || x == 37)
{
printf("AMEX\n");
}
else
{
printf("INVaLID\n");
}
}
}
else
{
printf("Invalid\n");
}
}
}
``````

and i cant use round here because if the number besides the decimal point is equal or greater than 5 , so the output will be increased by 1 than actual number.

You could just do `x = creditNumber % 100;` to get the last two digits.
And I think your maths is a bit flawed. When you are meant to add the digits of the doubled value (7*2 should result in 1+4=5), you seem to ignore that detail. Also, no need to handle `x < 10` separately.