C语言中的大数相乘问题

char *str1 = (char *)malloc(sizeof(char) * 100);
char *str2 = (char *)malloc(sizeof(char)* 100);
scanf("%s%s", str1, str2);
int len1 = strlen(str1);
int len2 = strlen(str2);
int len = len1 + len2 ;
int * sum = (int *)malloc(sizeof(int)* len);
memset(sum, 0, sizeof(int)* len);
int cc = 0; //填充零的计数
for (int i = len1 - 1; i >= 0; i--)
{

char * temp = (char *)malloc(sizeof(char)* len);
memset(temp, '0', sizeof(char)*len);
int tag = 0;
int count = len - 1;
int n = cc;
//进行相乘以后的填充
while (n > 0)
{
count--;
n--;
}

for (int j = len2 - 1; j >= 0; j--)
{
temp[count] = ((str1[i] - '0')  * (str2[j] - '0') + tag) % 10 + '0';
tag = ((str1[i] - '0')  * (str2[j] - '0') + tag) / 10;

count--;

}
// 处理有进位的情况
if (tag != 0)
{
temp[count] = tag + '0';

}
count--;
cc++;

int flag = 0;
//  int llen = strlen(temp);
for (int k = len - 1; k >= 0; k--)
{
int bb = (sum[k]) + (temp[k] - '0');
sum[k] = (bb + flag) % 10 ;

flag = (bb + flag) / 10;

}

}
//处理前面有零的情况
int kk = 0;
while (sum[kk] == 0)
{
kk++;
}
for (int i = kk; i < len; i++)
{
printf("%d", sum[i]);
}
printf("\n");