parse int to string

public class Solution {
    public int StrToInt(string str) {
        if (string.IsNullOrEmpty(str)) return 0;
        
        var sign = str[0] == '+' || str[0] == '-' ? 1 : 0;
        
        long result = 0;
        for (int i = sign; i < str.Length; i++) {
            if (!Char.IsDigit(str[i])) return 0;
            result = result * 10 + (str[i] - '0');
            
            if (sign == 1 && str[0] == '-') result = -result;
            if (result > Int32.MaxValue) return 0;
            if (result < Int32.MinValue) return 0;
        }
        
        return (int)result;
    }
}