8. String to Integer (atoi)

Total Accepted: 97070 Total Submissions: 721266 Difficulty: Easy

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.

Update (2015-02-10):
The signature of the C++ function had been updated. If you still see your function signature accepts a const char * argument, please click the reload button to reset your code definition.

Code:

int myAtoi(char* str) {
    if(!str)
        return 0;
    int sign = 1;
    int num = 0;
    while(*str == ' ')
        str++;
    if(*str == '+')
        str++;
    else if(*str == '-')
    {
        sign = -1;
        str++;
    }
    while(*str!='')
    {
        if(*str == '+'||*str == '-')
            return 0;
        else if(*str<'0'||*str>'9')
            return num*sign;
        if (num > INT_MAX / 10)
                return sign == 1? INT_MAX : INT_MIN;
            num*=10;
        if ((*str - '0') > (INT_MAX - num))
                return sign == 1? INT_MAX : INT_MIN;
        num = num + *str - '0';
        str++;
    }
    return num*sign;
}