PAT/PATAdvanced/1024.c

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

int isPalindromic(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;
}

char* reverse(char n[])
{
	char temp;
	int len = strlen(n);
	for (int i = 0; i < len / 2; i++) {
		temp = n[i];
		n[i] = n[len - i - 1];
		n[len - i - 1] = temp;
	}
	return n;
}

/* only works when a and b are of the same length */
void addAtoB(char a[], char b[])
{
	int l, s = 0, len = strlen(a);

	for (int i = 0; i < len; i++) {
		s += (a[i] - '0') + (b[i] - '0');
		l = s / 10;
		s %= 10;
		b[i] = s + '0';

		s = l;
	}

	if (s)
		b[len] = s + '0';
}

int main()
{
	int K, steps;
	char s1[100] = {0}, s2[100] = {0}, *n = s1, *m = s2;

	scanf("%s %d", n, &K);
	reverse(n);

	for (steps = 0; steps < K && !isPalindromic(n); steps++) {
		/* change 'm' into reverse of 'n' */
		strncpy(m, n, 100);
		reverse(m);
		/* add n and reversed n, and keep the result in n */
		addAtoB(m, n);
	}

	printf("%s\n%d", reverse(n), steps);

	return 0;
}