字符串转int——atoi函数模拟实现

#include<iostream>
#include<assert.h>
using namespace std;

int my_atoi(const char* s)
{
	int sign = 1;
	int res = 0;
	assert(s);
	if (*s == (const char)("\0"))
	{
		return 0;
	}
	int len = strlen(s);
	for (int i = 1; i < len; i++)
	{
		if (s[i] < '0' || s[i] > '9')
		{
			return 0;
		}
	}
	for (int i = 0; i < len; i++)
	{
		if (s[0] == '-')
		{
			sign = -1;
		}
		if (s[0] == '+')
		{
			sign = 1;
		}
		 if (s[i] >= '0' && s[i] <= '9')
		{
			res = res * 10 + (s[i] - '0');
		}
	}
	return sign*res;

}

int main()
{
	const char* p = "-1234";
	int res = my_atoi(p);
	cout << res << endl;  //输出-1234
	return 0;
}