还是A+B

#define _CRT_SECURE_NO_DEPRECATE
//计算A+B，如果A和B的末尾K位数相同，直接输出-1
//通过%，获取A和B的低K位，进行比较。可以边取边比较，如果还没到K位，可是A或者B已经为0，这时直接输出-1
//比较的同时进行逐位相加
#include<stdio.h>
#include<math.h>
int main()
{
	int A, B, K;
	int res;
	while (scanf("%d%d%d", &A, &B, &K) != EOF)
	{
		if (A == 0 && B == 0)
			break;
		res = 0;
		bool flag = false;
		int num = 0;
		int carray = 0;
		int e = 0;
		while (A != 0 || B != 0)
		{
			int a = A % 10;
			A /= 10;
			int b = B % 10;
			B /= 10;
			if (a == b)
			{
				num++;
				if (num == K || A == 0 || B == 0)
				{
					flag = true;
					break;
				}
			}
			int sum = a + b+ carray;
			res += (sum%10)*pow(10,e++);
			carray = sum / 10;
		}
		if (carray != 0)
			res += carray * pow(10, e);
		if (flag == true)
			printf("-1\n");
		else
			printf("%d\n", res);
	}
	return 0;

}