大整数的乘法

使用字符串来模拟实现两个大整数的乘法！

void  maxIM(char *num1, int x1, char *num2, int x2)
{
    char *re = (char *)malloc(x1+x2);
    char *an1 = (char *)malloc(x1 );
    char *an2 = (char *)malloc(x2 );
    memset(re, 0, x1+x2);
    memset(an1, 0, x1);
    memset(an2, 0, x2);
    int m=0;

    for(int i = x1 - 1; i>=0; i--)
        an1[m++] = num1[i] - '0';

    m = 0;

    for(int j = x2 - 1; j>=0; j--)
        an2[m++] = num2[j] - '0';

    for(int i = 0; i < x2; i++)
        for(int j = 0; j < x1; j++)
        {
            re[i+j] += an2[i]*an1[j];
        }
    for(int i = 0; i < x1+x2;i++)
    {
        if(re[i]>=10)
        {
            re[i+1] += re[i]/10;
            re[i] = re[i]%10;
        }
    }
    bool startOutPut = false;
    for(int i = x1 + x2 - 1; i>=0; i--)
    {
        if(startOutPut)
            printf("%d", re[i]);
        else if(re[i])    
        {
            printf("%d", re[i]);
            startOutPut = true;
        }
    }
    if(!startOutPut)
        printf("0");
    printf("\n");
}