Thread: Airline ticket problem

>however when I enter the number 47715497443 (which is the test number) it gives off a not valid entry

Integer overflow?

Code:

#include <stdio.h>
#include <limits.h>

int main(void)
{
   printf("%d\n", INT_MAX);
   puts("47715497443");
   return 0;
}

/* my output
2147483647
47715497443
*/

Originally posted by CrackerJack

Code:

#include <stdio.h>

main ()
{

int ch=0, last=0;
int num=0;
int ticketval=0;

	printf("Enter ticket number: ");
	while ( ( ch = getchar() ) != '\n' )
	{
		ticketval = ch - '0' + (ticketval * 10);
		num = ch;
all you've done with num is load a useless value into it.
What I was trying to get you to you've almost got, so...
		num = ch - '0';    // convert the character to a number
		ticketval = num + (ticketval * 10);  


	}
	last = num - 48;  // kill this line, you won't need it 

// finally, you get to fix this IF based on the above
	if ( (ticketval % 7) == last ) 
		printf("VALID \n");
	else
		printf("Not a valid ticket! \n");

}

Well that seemed to work for some numbers, but not all of the ones I tried. Man I am really confused on what other way to do this!!!

WHAT AM I MISSING HERE? :Bangs head against wall:

>I tried changing it to long int instead (b/c I thought that allowed for more numbers)

Not necessarily.

Code:

#include <stdio.h>
#include <limits.h>

int main(void)
{
   printf("%d\n",  INT_MAX);
   printf("%ld\n", LONG_MAX);
   puts("47715497443");
   return 0;
}

/* my output
2147483647
2147483647
47715497443
*/

For a number of that size, you may have to switch to a double, which would mean the % operator won't work.

Just out of interest CJ, can you elaborate on how your teacher suggested you do it?

If the ticket number is that large, then you may as well use a char array instead of an int. It's not like you're going to want to perform calculations with it anyway, eh, other than the mod validation.

Originally posted by Hammer
If the ticket number is that large, then you may as well use a char array instead of an int. It's not like you're going to want to perform calculations with it anyway, eh, other than the mod validation.

Now you got me. How do you perform a mod on a char array?

Anyway, the fmod() function is standard so you can use that on a float

Originally posted by WaltP
Now you got me. How do you perform a mod on a char array?

Code:

#include <stdio.h>
#include <string.h>

#define MOD_BY 7

int mymod(char *data, size_t length)
{
  int num = 0;
  while (length--)
  {
    num = ((num * 10) + (*data++ - '0')) % MOD_BY;
  }
  return num;
}

int main(void)
{
  char account[] = "4771549744";
  
  printf ("%s mod %d is %d\n", account, MOD_BY, mymod(account, strlen(account)));
  
  return(0);
}

That's kool! Thanks Hammer