String to Integer (atoi).cpp

class Solution {
public:
    int atoi(const char *str) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if(*str=='\0') return 0; 
        while(*str==' ') str++;
        bool negative=false;
        if(*str=='-')
        {
            negative=true; str++; 
        }else if(*str=='+')
        {
            str++;
        }
        int result=0; 
        while(*str<='9' && *str>='0')
        {
            if((INT_MAX-(*str-'0'))/10<result)
            {
                return negative? INT_MIN:INT_MAX; 
            }
            result=10*result+*str-'0';
            str++; 
        }
        return negative? -result:result; 
    }
};

String to Integer (atoi).java

public class Solution {
    public int atoi(String str) {
        // Start typing your Java solution below
        // DO NOT write main() function
        int length=str.length(); 
        if(length==0) return 0; 
        int index=0; boolean negative=false; int result=0; 
        while(str.charAt(index)==' ')
        {
            index++; 
        }
        if(str.charAt(index)=='-') 
        {
            negative=true; index++; 
        }else if(str.charAt(index)=='+')
        {
            negative=false; index++; 
        }
        for(; index<length; index++)
        {
            if(str.charAt(index)>='0' && str.charAt(index)<='9')
            {
            if(result<=(Integer.MAX_VALUE-(str.charAt(index)-'0'))/10)
            {
                result=result*10+str.charAt(index)-'0';
            }else return negative? Integer.MIN_VALUE: Integer.MAX_VALUE; 
            }
            else break; 
        }
        return negative? -result: result; 
    }
}