剑指offer(替换空格)

请实现一个函数，将一个字符串中的每个空格替换成“%20”。例如，当字符串为We Are Happy.则经过替换之后的字符串为We%20Are%20Happy。

void replaceSpace(char *str, int length)
{
    //记录空格出现的个数,申请一个等长的数组,用来暂时存储原数组
    int times = 0;
    char sstr[length];
    for (int i = 0; i < length; ++i)
    {
        sstr[i] = str[i];
        if (str[i] == ' ')
        {
            times++;
        }
    }

    //数组扩容
    int len = length + (times * 2);
    str = (char *)realloc(str, sizeof(char) * len);

    //寻找插入位置
    int p = 0;
    int q = 0;
    while (p < length)
    {
        if (sstr[p] != ' ')
        {
            str[q] = sstr[p];
            ++p;
            ++q;
        }
        else
        {
            str[q++] = '%';
            str[q++] = '2';
            str[q++] = '0';
            p++;
        }
    }
}