char a[] = "1234567899987654321";
char b[] = "9874561231236547898";
char c[] = "0000000000000000000";
	/* Asserting that len(a) == len(b) */
int i = 0;
int carry = 0;
int a_index = 0;
int b_index = 0;
int add_result = 0;
for ( i = strlen(a) ; i > 0; --i ) {
	a_index = (int)a[i-1] - 0x30;
	b_index = (int)b[i-1] - 0x30;
	add_result = a_index + b_index + carry;
	if (10 <= add_result) {
			/* Not sure how neccesary this is */
		carry = add_result / 10;
		add_result = add_result - (10*carry);
	}
	c[i-1] = (char)(add_result + 0x30)
}
printf("%s", c);