String to Integer (atoi) Implement atoi to convert a string to an integer. Hint: Carefully consider all possible input cases. If you want a challenge, please do not see below and ask yourself what are the possible input cases. Notes: It is intended for this problem to be specified vaguely (ie, no given input specs). You are responsible to gather…

atoi.cpp

// atoi.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include <iostream>

using namespace std;

class Solution 
{
public:
	int atoi(const char *str) 
	{
		bool positive = true;
		if (str == NULL)
			return 0;

		int i = 0;
		int result = 0;


		while ((str[i] != NULL) && ((str[i] == ' ') || (str[i] == '\t') || (str[i] == '\n') || (str[i] == '\r')))
			i++;

		if (str[i] == '-')
		{
			positive = false;
			i++;
		}
		else if (str[i] == '+')
		{
			positive = true;
			i++;
		}

		while (str[i] != NULL)
		{
			// Hit invalid char
			if ((str[i] < '0') || (str[i] > '9'))
				break;

			if ((2147483647 - (str[i] - '0')) / 10 < result)
			{
				result = (positive) ? 2147483647 : -2147483648;
				break;
			}

			result = result * 10 + (str[i] - '0');

			i++;
		}

		return (positive) ? result : -1 * result;
	}
};

int _tmain(int argc, _TCHAR* argv[])
{
	Solution s;
	int result = 0;
	char *input = NULL;

	input = NULL;
	result = s.atoi(input);
	cout << ((input == NULL) ? "" : input) << " -- " << result << endl;

	input = "";
	result = s.atoi(input);
	cout << ((input == NULL) ? "" : input) << " -- " << result << endl;

	input = "0";
	result = s.atoi(input);
	cout << ((input == NULL) ? "" : input) << " -- " << result << endl;

	input = "-0";
	result = s.atoi(input);
	cout << ((input == NULL) ? "" : input) << " -- " << result << endl;

	input = "1";
	result = s.atoi(input);
	cout << ((input == NULL) ? "" : input) << " -- " << result << endl;

	input = "-1";
	result = s.atoi(input);
	cout << ((input == NULL) ? "" : input) << " -- " << result << endl;

	input = "+1";
	result = s.atoi(input);
	cout << ((input == NULL) ? "" : input) << " -- " << result << endl;

	input = "   1";
	result = s.atoi(input);
	cout << ((input == NULL) ? "" : input) << " -- " << result << endl;

	input = "     -1";
	result = s.atoi(input);
	cout << ((input == NULL) ? "" : input) << " -- " << result << endl;

	input = "     +11";
	result = s.atoi(input);
	cout << ((input == NULL) ? "" : input) << " -- " << result << endl;

	input = "123";
	result = s.atoi(input);
	cout << ((input == NULL) ? "" : input) << " -- " << result << endl;

	input = "q123";
	result = s.atoi(input);
	cout << ((input == NULL) ? "" : input) << " -- " << result << endl;

	input = "123q";
	result = s.atoi(input);
	cout << ((input == NULL) ? "" : input) << " -- " << result << endl;

	input = "123e456";
	result = s.atoi(input);
	cout << ((input == NULL) ? "" : input) << " -- " << result << endl;

	input = "-+123q";
	result = s.atoi(input);
	cout << ((input == NULL) ? "" : input) << " -- " << result << endl;

	input = "2147483648";
	result = s.atoi(input);
	cout << ((input == NULL) ? "" : input) << " -- " << result << endl;

	input = "-2147483648";
	result = s.atoi(input);
	cout << ((input == NULL) ? "" : input) << " -- " << result << endl;

	input = "-2147483649";
	result = s.atoi(input);
	cout << ((input == NULL) ? "" : input) << " -- " << result << endl;

	input = " -11919730356x";
	result = s.atoi(input);
	cout << ((input == NULL) ? "" : input) << " -- " << result << endl;

	input = " 10522545459";
	result = s.atoi(input);
	cout << ((input == NULL) ? "" : input) << " -- " << result << endl;

	return 0;
}