主要內容：針對於字串的基本操作：字串逆序、獲取最長單詞、數字字元轉數字、數字轉字串、十六進位制字串轉十進位制數

 //字串逆置
void Reverse_str(char *str) 
{
	char *p;
	for(p=str;*p!='\0';p++) ;

	char tmp;
	p--;
	while(str < p)//str != p
	{
		tmp = *str;
		*str = *p;
		*p = tmp;
		str++;
		p--;
	}
}

//字串轉數字
int Myatoi(const char *str)//"123a45"->123,"a123"->0
{
	int sum = 0;
	while(isdigit(*str))
	{
		sum = sum*10 + (*str-'0');
		str++;
	}
	return sum;
}

char *Myitoa(int n)//error
{
	char str[100];

	return str;
}


//數字轉字串
void Myitoa(char *str,int n)//12345->"54321"->"12345"
{
	int i = 0;
	do
	{
		str[i++] = n%10 + '0';
		n /= 10;
	}while(n != 0);
	str[i] = '\0';

	Reverse_str(str);
}


//獲取最長的單詞，記憶體有函式建立，使用完後請注意釋放記憶體
char *MaxWord(const char *str)
{
	int len = strlen(str);
	char *str1 = (char *)malloc((len+1)*sizeof(char));//存放當前單詞
	char *str2 = (char *)malloc((len+1)*sizeof(char));//存放最長單詞
	int cur = 0; // 當前單詞的長度
	int max = 0;//最長單詞的長度
	while(*str != '\0')
	{
		if(isalpha(*str))
		{
			str1[cur++] = *str;
		}
		else
		{
			if(cur > max)
			{
				str1[cur] = '\0';
				strcpy(str2,str1);//將當前單詞拷貝到最長單詞
			}
			cur = 0;
		}
		str++;
	}
	//bug
	free(str1);
	return str2;
}


//十六進位制字串轉十進位制數
int HexToi(const char *str)      //"0x1b"->27,"0x123"->291
{
	int tmp = 0;
	if(str[0]!='0' || str[1]!='x'&&str[1]!='X')
	{
		return 0;
	}
	str += 2;
	while(isxdigit(*str))
	{
		if(isdigit(*str))
		{
			tmp = tmp*16 + (*str-'0');
		}
		else // 字母,大寫，小寫
		{
			tmp = tmp*16 + (tolower(*str)-'a'+10);
		}
		str++;
	}
	return tmp;
}

int main()
{
	int a = HexToi("0x1234");
	int b = HexToi("0X12ab");
	int c = HexToi("0x12AB");
	int d = HexToi("12ab");
	int e = HexToi("0x12gh");
	printf("%d,%x\n",a,a);
	printf("%d,%x\n",b,b);
	printf("%d,%x\n",c,c);
	printf("%d,%x\n",d,d);
	printf("%d,%x\n",e,e);
	//char *p = MaxWord("asdf ad ewrt ,adffad,awqwerrt");
	//printf("%s\n",p);
	//free(p);
	//char str[20];
	//Myitoa(str,123456789);
	//Myitoa(str,0);
    //printf("%s\n",str);
	//printf("%d\n",atoi("1234567"));
	//printf("%d\n",atoi("1234a567"));
	//printf("%d\n",atoi("    1234"));
	//printf("%d\n",atoi("a1234567"));
	//printf("%d\n",atoi("1234567890987654321"));
	//printf("%d\n",atoi("-1234567"));//
	/*char str1[] = "abcd";
	Reverse_str(str1);
	printf("%s\n",str1);*/

	return 0;
}