char FirstNotRepeatingChar(char* pString){    // invalid input    if(!pString)        return 0;    // get a hash table, and initialize it    const int tableSize = 256;                    //字符1个字节8位    unsigned int hashTable[tableSize];          //unsigned？？    for(unsigned int i = 0; i < tableSize; ++ i)        hashTable[i] = 0;                        //为什么要置0？    // get the how many times each char appears in the string    char* pHashKey = pString;    while(*(pHashKey) != ‘\0‘)        hashTable[*(pHashKey++)] ++;    // find the first char which appears only once in a string    pHashKey = pString;    while(pHashKey)    {        if(hashTable[*pHashKey] == 1)            return *pHashKey;        pHashKey++;    }    // if the string is empty    // or every char in the string appears at least twice    return 0;}