Thread: validate isbn

hey ,guys,i'm stuck trying to validate a ISBN number(w/o hyphens). I want it to check the last digit for a X and update the sum. But i keep getting the wrong sum. What's wrong in my code?

[code]
#include<stdio.h>
#include<ctype.h>

Code:

int testISBN(char*);

int main (void)
{
	int divisible;
	char choice, trash;
	char code[15];

	do
	{
		printf("Enter an ISBN (book) number:\n");
		fgets(code,15,stdin);

		printf("The ISBN entered is:%s\n",code);
		divisible = testISBN(code);
		if (divisible == 1)
					printf("\n\n\tValid ISBN Number\n");
		else
					printf("\n\n\tInvalid ISBN Number\n");
			
		printf("\nDo you wish to continue? (Y/N)\n");
		choice = getchar();
		trash = getchar();
	}while(toupper(choice) != 'N');
	
	return 0;
}

int testISBN(char*code)
{
	int i;
	int sum = 0;
	int value;

	for(i=9;i>=0; i--)
	{
		if((i==9) && (toupper(*(code + i)) == 'x'))
			{
				value = 10;
			}
		else
			{
				value = (int)(*(code + i)-48);
			}
		sum += value * (i+1);
	}
	printf("sum is %d",sum);
	
	if ((sum%11) == 0)
		return 1;
	return 0;
}