注意上溢和下溢問題
num Status {kValid =0,kInvalid};
int g_nStatus = kValid;
long long StrToIntCore(const char* digit,bool minus)
{
long long num =0;
while(*digit != '\0')
{
if(*digit >= '\0' && *digit <= '9')
{
int flag = minus ? -1 : 1;
num = num * 10 + flag * (*digit - '0');
if((!minus && num > 0x7fffffff) || (minus && num < (signed int)0x80000000))
{
num = 0;
break;
}
digit++;
}
else
{
num = 0;
break;
}
}
if(*digit == '0')
{
g_nStatus = kValid;
}
return num;
}
int StrToInt(const char* str)
{
g_nStatus = kInvalid;
long long num =0;
if(str != NULL && *str != '\0')
{
bool minus = false;
if(*str == '+')
str++;
else if(*str == '-')
{
str++;
minus = true;
}
if(*str != '\0')
{
num = StrToIntCore(str,minus);
}
}
return (num);
}
void Test(char* string)
{
int result = StrToInt(string);
if(result == 0 && g_nStatus == kInvalid)
printf("the input %s is invalid.\n", string);
else
printf("number for %s is: %d.\n", string, result);
}
int main()
{
Test(NULL);
Test("");
Test("123");
Test("+123");
Test("-123");
Test("1a33");
Test("+0");
Test("-0");
Test("+2147483647");
Test("-2147483647");
Test("+2147483648");
Test("-2147483648");
Test("+2147483649");
Test("-2147483649");
Test("+");
Test("-");
return 0;
}