PAT/PATBasic/1079.c

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

int isPalindromicNumber(char n[])
{
	int len = strlen(n);
	for (int i = 0; i < len / 2; i++)
		if (n[i] != n[len - i - 1])
			return 0;
	return 1;
}

void addBtoA(char a[], char b[])
{
	/* Assume length of a and b are the same */
	int len = strlen(a), sum, carry = 0;
	for (int i = len - 1; i >= 0; i --) {
		sum = a[i] - '0' + b[i] - '0' + carry;
		a[i] = sum % 10 + '0';
		carry = sum / 10;
	}
	if (carry) { /* Length of a + b is larger than a or b */
		memmove(a + 1, a, len + 1); /* Shift to right by 1 */
		a[0] = carry + '0';         /* Add the carry to beginning */
	}
}

void reverseAtoB(char a[], char b[])
{
	int len = strlen(a);
	for (int i = 0; i < len; i++)
		b[len - i - 1] = a[i];
}

int main()
{
	int i;
	char a[1011] = {0}, b[1011] = {0};

	scanf("%s", a);
	for (i = 0; i < 10 && !isPalindromicNumber(a); i++) {
		reverseAtoB(a, b);
		printf("%s + %s = ", a, b);
		addBtoA(a, b);
		printf("%s\n", a);
	}

	if (i == 10)
		printf("Not found in 10 iterations.");
	else
		printf("%s is a palindromic number.", a);

	return 0;
}