将一个字符串转换成一个整数，要求不能使用字符串转换整数的库函数。 数值为0或者字符串不是一个合法的数值则返回0

// test20.cpp : 定义控制台应用程序的入口点。
//

include "stdafx.h"

include

include

include

include

include

include

include<string.h>

include

using namespace std;

class Solution {
public:
int StrToInt(string str) {
//如果字符串为空，返回-1
if (str == "")return 0;
int num=0;//要输出的数字
int flag=1;//符号位，0表示负数，1表示正数
cout << str.find_first_not_of("1234567890+-") << endl;
if (str.find_first_not_of("1234567890+-") < str.size()) return 0;//如果存在不合法字符

char ch = str[0];
int i = 0;
//判断符合
if (ch == '-')
{
flag = 0;//数字为负数
i = 1;
}
else if (ch == '+')
{
flag = 1;//为正数
i = 1;
}
else
{
i = 0;
}

while (i<str.size())
{
// cout << "str[i]:" << str[i] << endl;
int a = str[i]-48; //char类型和int类型相差48
// cout << "a:" << a << endl;
num = num * 10 + a;
cout << "num:" << num << endl;
i++;
}

if (flag == 0) num = -num;

return num;
}
};

int main()
{

Solution so;
//int count = so.FirstNotRepeatingChar("wangdanwang");
vector data = { 1,2,3,4,5,5,5,6,7,8};
int count = so.StrToInt("123");
cout << count << endl;

cout << endl;
return 0;
}