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// Source : https://oj.leetcode.com/problems/string-to-integer-atoi/

// Author : Hao Chen

// Date : 2014-06-18

/**********************************************************************************

* 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 all the input requirements up front.

* Requirements for atoi:

* The function first discards as many whitespace characters as necessary until the first

* non-whitespace character is found. Then, starting from this character, takes an optional

* initial plus or minus sign followed by as many numerical digits as possible, and interprets

* them as a numerical value.

* The string can contain additional characters after those that form the integral number,

* which are ignored and have no effect on the behavior of this function.

* If the first sequence of non-whitespace characters in str is not a valid integral number,

* or if no such sequence exists because either str is empty or it contains only whitespace

* characters, no conversion is performed.

* If no valid conversion could be performed, a zero value is returned. If the correct value

* is out of the range of representable values, INT_MAX (2147483647) or INT_MIN (-2147483648)

* is returned.

**********************************************************************************/

#include <stdio.h>

#include <stdlib.h>

#include <ctype.h>

#define INT_MIN (-2147483647 - 1)

#define INT_MAX 2147483647

int atoi(const char *str) {

if (str==NULL || *str=='\0'){

return 0;

}

int ret=0;

for(;isspace(*str); str++);

bool neg=false;

if (*str=='-' || *str=='+') {

neg = (*str=='-') ;

str++;

}

for(; isdigit(*str); str++) {

int digit = (*str-'0');

if(neg){

if( -ret < (INT_MIN + digit)/10 ) {

return INT_MIN;

}

}else{

if( ret > (INT_MAX - digit) /10 ) {

return INT_MAX;

}

ret = 10*ret + digit ;

}

return neg?-ret:ret;

}

int main()

{

printf("\"%s\" = %d\n", "123", atoi("123"));

printf("\"%s\" = %d\n", " 123", atoi(" 123"));

printf("\"%s\" = %d\n", "+123", atoi("+123"));

printf("\"%s\" = %d\n", " -123", atoi(" -123"));

printf("\"%s\" = %d\n", "123ABC", atoi("123ABC"));

printf("\"%s\" = %d\n", " abc123ABC", atoi(" abc123ABC"));

printf("\"%s\" = %d\n", "2147483647", atoi("2147483647"));

printf("\"%s\" = %d\n", "-2147483648", atoi("-2147483648"));

printf("\"%s\" = %d\n", "2147483648", atoi("2147483648"));

printf("\"%s\" = %d\n", "-2147483649", atoi("-2147483649"));

return 0;

}

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