两个都是数目字的字符串求和

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

void add(char *a, char *b)
{
	char *ret,*array_a,*array_b;
	int lena,lenb,len_small,len_big,i,tmp = 0;/*tmp表示是否有进位*/

	if(a == NULL || b == NULL)
		return;

	lena = strlen(a);
	lenb = strlen(b);
	len_small = (lena > lenb) ? lenb:lena;
	len_big = (lena < lenb) ? lenb:lena;

	if ((array_a = malloc(lena)) == NULL)
		goto out;
	for(i = 0; i < lena; i++)
	{
		array_a[lena - i - 1] = a[i] - '0';
	}
	
	if ((array_b = malloc(lenb)) == NULL)
		goto out;
	for(i = 0; i < lenb; i++)
	{
		array_b[lenb - i - 1] = b[i] - '0';
	}
	
	ret = malloc(len_big + 1);
	if(ret == NULL)
		goto out;

	/*把低位相加*/
	for(i = 0; i < len_small; i++)
	{
		tmp += array_a[i] + array_b[i];
		ret[i] = (tmp % 10) + '0';
		tmp = tmp / 10;
	}

	/*如果有高位的话，在把高位相加*/
	if(lena > lenb)
	{
		for(i;  i < len_big; i++)
		{
			tmp += array_a[i];
			ret[i] = (tmp % 10) + '0';
			tmp = tmp / 10;
		}
	}
	else
	{
		for(i;  i < len_big; i++)
		{
			tmp += array_b[i];
			ret[i] = (tmp % 10) + '0';
			tmp = tmp / 10;
		}
	}

	if(tmp)/*如果最后有进位*/
		ret[i] = tmp + '0';	
	else
		i--;

	/*从高位开始打印*/
	for(i; i >= 0 ; i--)
	{	
		printf("%c",ret[i]);
	}
	printf("\n");

out:
	if (array_a)
		free(array_a);
	if(array_b)
		free(array_b);
	if(ret)
		free(ret);
}

int main(int argc, char *argv[])
{
	char *a = "55552342423535345";
	char *b = "55555";

	add(a ,b);

	return 0;
}