[LeetCode #8] 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 all the input requirements up front.

int myAtoi(char *s){
    int ret = 0;
    int i = 0;
    int digit = 0;
    int sign = 1;

    while(s[i] && s[i] == ' '){ i++; }
    if (s[i] == '+') {sign = 1; i++;}
    else if (s[i] == '-') {sign = -1; i++;}
    
    while (s[i]){
        if ((s[i] <= '9') && (s[i] >= '0')){
            digit = s[i] - '0';
        }
        else{
            break;
        }
        if(2147483647/10 < ret || 2147483647/10 == ret && 2147483647%10 < (s[i] -'0')) 
        {
            return sign == -1 ? (-2147483648) : 2147483647;
        } 
        ret = ret * 10 + digit;  
        i++;
    }    
    return ret * sign;
}