C語言實驗——合法的C識別符號

Problem Description

Input

Output

Sample Input

123You

Sample Output

NO

Hint

//package hello;
import java.util.Scanner;
public class Main {  
    
    public static void main(String[] args) {  
        Scanner cin = new Scanner(System.in);  
        String str = cin.next();
        char ch;
        int len = str.length();
        ch = str.charAt(0);
        if(ch >= '0' && ch <= '9')
        	System.out.println("NO");
        else {
        	int i;
        	for(i = 0; i < len; i++) {
            	ch = str.charAt(i);
            	if(i == 0) {
            		if((ch>='a'&&ch<='z') || (ch>='A'&&ch<='Z') || ch=='_')
            			continue;
            		else
            			break;
            	}
      
            	if(i != 0) {
            		if((ch>='a'&&ch<='z') || (ch>='A'&&ch<='Z') || (ch>='0'&&ch<='9') || ch=='_')
            			continue;
            		else 
            			break;
            	}
            }
        	if(i >= len) {
        		System.out.println("YES");
        	}
        	else {
        		System.out.println("NO");
        	}
        }
    }  
}