C language force buckle the eighth question of string conversion integer. Ergodic method

Please come to realize a myAtoi(string s) function , Enable it to convert a string to a 32 Bit signed integer （ similar C / C++ Medium atoi function ）.

function myAtoi(string s) The algorithm is as follows ：

Read in strings and discard useless leading spaces
Check the next character （ Suppose you haven't reached the end of the character yet ） Positive or negative , Read the character （ If there is ）. Determine whether the final result is negative or positive . If neither exists , Suppose the result is positive .
Read in the next character , Until you reach the next non numeric character or the end of the input . The rest of the string will be ignored .
Convert the numbers read in the previous steps into integers （ namely ,"123" -> 123, "0032" -> 32）. If you don't read in the numbers , Then the integer is 0 . Change the symbol if necessary （ From step 2 Start ）.
If the number of integers exceeds 32 Bit signed integer range [−2^31, 2^31 − 1] , You need to truncate this integer , Keep it in this range . say concretely , Less than −2^31 The integer of should be fixed to −2^31 , Greater than 2^31 − 1 The integer of should be fixed to 2^31 − 1 .
Returns an integer as the final result .

Be careful ：

The white space character in this question only includes the space character ' ' .
Except for the leading space or the rest of the string after the number , Do not ignore Any other character .

Example 1：

Input ：s = "42"
Output ：42
explain ： The bold string is the character that has been read in , The caret is the character currently read .
The first 1 Step ："42"（ No characters are currently read in , Because there are no leading spaces ）
The first 2 Step ："42"（ No characters are currently read in , Because it doesn't exist here '-' perhaps '+'）
The first 3 Step ："42"（ Read in "42"）
Parse to get an integer 42 .
because "42" In scope [-231, 231 - 1] Inside , The final result is 42 .

Example 2：

Input ：s = "   -42"
Output ： - 42
explain ：
The first 1 Step ："   -42"（ Read in leading space , But ignore ）
The first 2 Step ："   -42"（ Read in '-' character , So the result should be negative ）
The first 3 Step ："   -42"（ Read in "42"）
Parse to get an integer - 42 .
because "-42" In scope [-231, 231 - 1] Inside , The final result is - 42 .

Example 3：

Input ：s = "4193 with words"
Output ：4193
explain ：
The first 1 Step ："4193 with words"（ No characters are currently read in , Because there are no leading spaces ）
The first 2 Step ："4193 with words"（ No characters are currently read in , Because it doesn't exist here '-' perhaps '+'）
The first 3 Step ："4193 with words"（ Read in "4193"; Because the next character is not a number , So read in stop ）
Parse to get an integer 4193 .
because "4193" In scope [-231, 231 - 1] Inside , The final result is 4193 .

source ： Power button （LeetCode）
link ：https ://leetcode.cn/problems/string-to-integer-atoi
Copyright belongs to the network . For commercial reprint, please contact the official authority , Non-commercial reprint please indicate the source .

  Numbers 0 To 9 Of ASCII The code values are respectively 48 To 57;
Pay attention to three points 1. Minus question 2. Spillover problem 3. Illegal character judgment

#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <string.h>

int test(char * s) 
{
	int out = 0;// Output 
	int len = strlen(s);// String length 
	int i = 0;// Traverse the parameters of the string 
	int pos = 1;// Judge positive and negative , If there is no positive or negative, the default is 1, That is, the default positive number 
	int max = 2147483647;
	int min = -max - 1;
	if (len == 0)
		return 0;
	while (s[i]<'0'||s[i]>'9')// Loop the non numeric characters before 
	{
		if (s[i] == ' '||((s[i]<'0' || s[i]>'9')&&s[i]!='+'&&s[i] != '-'))// If it is a space, continue to the next 
			i++;
		if (s[i] == '-')// Judge whether it is a negative number 
		{
			pos = -1;
			i++;
		}
		if (s[i] == '+'&&pos == 1)// Determine whether it is a positive number   And throw it away “+-12” The impact of such situations 
		{
			pos = 1;
			i++;
		}
		if (s[i] == '+'&&pos == -1)// Determine whether it is a positive number   And throw it away “+-12” The impact of such situations 
		{
			pos = -1;
			i++;
		}
	}
	while (s[i + 1]>='0' && s[i + 1]<='9')
	{
		out = out * 10 + s[i] - '0';
		i++;
	}
	out = pos * out;
	// The following is to judge whether it overflows 
	if (out > 0)
	{
		if (out > max / 10 || (out == max / 10 && (s[i] - '0') > max % 10))
			return max;
		else
			out = out * 10 + s[i] - '0';
	}
	if (out < 0)
	{
		if (out < min / 10 || (out == min / 10 && ('0' - s[i]) < min % 10))
			return min;
		else
			out = out * 10 - s[i] + '0';
	}
	return out;
}

int test2(char * s) {
	int i = 0;
	int out = 0;
	int pol = 1;
	int len = strlen(s);

	if (len == 0) return 0;

	while (s[i] == ' ') i++;  // Delete the blank space 
	if (s[i] == '-') {         // Judge positive and negative 
		pol = -1;
		i++;
	}
	else if (s[i] == '+') {
		pol = 1;
		i++;
	}
	else {
		pol = 1;
	}

	while (s[i] != '\0') {
		if (s[i]<'0' || s[i]>'9') { // Illegal character check 
			i++;
			break;
		}
		if (out > INT_MAX / 10) return (pol > 0 ? INT_MAX : INT_MIN);  // Cross border judgment 
		if (out == INT_MAX / 10) {
			if (pol > 0 && s[i] > '7') return INT_MAX;
			else if (pol < 0 && s[i] >= '8') return INT_MIN;
		}
		// The following should be written normally out=10*out+(s[i]-'0'), The reason for subtracting '0',
		// To prevent 10*out+s[i] Transboundary 
		out = 10 * out - '0' + s[i];
		// Because this topic is not allowed 64 Bit stored data , So illegal judgment can be simpler 
		// You can directly out Defined as long type , Just judge directly 
		//if(pol*out>INT_MAX) return INT_MAX;
		//if(pol*out<INT_MIN) return INT_MIN;
		i++;
	}
	out = out * pol;

	return out;
}
int main()
{
	char s[20] = "wwww  -42";
	//printf("%d", strlen(s));
	int out = 0;
	//out = test(s);
	out = test2(s);
	printf("%d", out);

	return 0;
}

another ： My test The function cannot pass the force deduction . The output displayed on the force buckle is 0, But in vs The compiler has no problems with any of the samples , Is there a boss to guide the problem ...