思路：拆分在合併，有非數字符號的return 0;
public class _Test49 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String string = scanner.nextLine();
        System.out.println(strToInt(string));

    }
    public static int strToInt(String string){
        int result = 0
 
;
        if (string == null && string.isEmpty()) {
            return 0;
        }
        int i = 0;
        if (string.charAt(0) == '+'||string.charAt(0) == '-') {
            i = 1;
        }
        for (; i < string.length(); i++) {
            char c = string.charAt(i);
            if (c <= '9'
 
 && c >= '0') {
                int a = c - '0';
                result = result * 10 + a;                
            }
            else{
                return 0;
            }
        }
        if (string.charAt(0) == '-') {
            result = -result;
        }           
        return result;
    }

}