將字串轉換成為整數，要注意邊界問題，比如說要轉換的整數超過了最大的整數，還有處理空字串的情況。

#include <iostream>
#include <string>

using namespace std;

//列舉型的值判斷值是否有效
enum {kValid = 0, kInvalid};

int status = kValid;

long long StrToIntCore(char *str, bool minus)
{
	long long num = 0;
	while (str != NULL && *str != '\0')
	{
		if (*str >= '0' && *str <= '9')
		{
			int flag = minus ? 1 : -1;
			num = num * 10 + flag * (*str - '0');
			//32位有符號整數的最大值0X7FFFFFFF, 最小整數0X80000000
			if ((minus && num > 0x7FFFFFFF) || (!minus && num < (signed int)0x80000000))
			{
				num = 0;
				break;
			}
			++str;
		}
		else
		{
			num = 0;
			break;
		}
	}
	if (*str == '\0')
	{
		status = kValid;
	}
	return num;
}

int StrToInt(char *str)
{
	status = kInvalid;
	long long num = 0;
	if (str != NULL && *str != '\0')
	{
		//true為正，false為負
		bool minus = true;
		if (*str == '+')
			str++;
		if (*str == '-')
		{
			str++;
			minus = false;
		}
		if (*str != '\0')
		{
			num = StrToIntCore(str, minus);
		}
	}
	return (int)num;
}

int main()
{
	char str[] = "-1";
	int num = StrToInt(str);
	cout << num;
}