数据结构练习（15）把字符串转换成整数

#include <iostream>
#include <cstdio>
using namespace std;

bool str2int(const char *b, int& num)
{
if (b == NULL)
return false;

long long n = 0;
bool minus = false;
const char *s = b;

if (*s == '+')
++s;
else if (*s == '-')
++s, minus = true;

while (*s != '\0')
{
if ('0' <= *s && *s <= '9')
{
n = n * 10 + *s - '0';
if (n > numeric_limits<int>::max())
return false;
++s;
}
else
return false;
}
if (minus)
n = 0 - n;
num = n;
return true;
}

int main()
{
char b[20];
gets(b);
int num;
bool flag = str2int(b, num);
if (flag)
printf("%d\n", num);
else
printf("error\n");
return 0;
}