1134: Legal C identifier query

Method 1 ： Write directly according to the meaning of the title , Easy to understand

#include<string.h>
#include<iostream>
using namespace std;
int main()
{
	char a[300];	
    cin.getline(a,300);
    int len=strlen(a);
    if(a[0]>='0'&&a[0]<='9')
     {
     	cout<<"no";
     	return 0;
	 }
    for(int i=0;i<len;i++)
    {
    	if(((a[i]>='0'&&a[i]<='9')||(a[i]>=65&&a[i]<=90)||(a[i]>=97&&a[i]<=122)||a[i]=='_'))
    	{
    		;
		}
		else
		{
			cout<<"no";
			return 0;
		}
		
	}
	cout<<"yes";
	 return 0;
}

Method 2 ： Similar to method 1

#include<string.h>
#include<iostream>
using namespace std;
int main()
{
	char a[300];	
    cin.getline(a,300);
    int len=strlen(a);
    if(a[0]>='0'&&a[0]<='9')
     {
     	cout<<"no";
     	return 0;
	 }
    for(int i=0;i<len;i++)
    {
    	if(!((a[i]>='0'&&a[i]<='9')||(a[i]>=65&&a[i]<=90)||(a[i]>=97&&a[i]<=122)||a[i]=='_'))
    	{
    		cout<<"no";
    	    return 0;
		}
	}
	cout<<"yes";
	 return 0;
}

Method 3 ： Do not convert letters to asscii The corresponding number in

#include<string.h>
#include<iostream>
using namespace std;
int main()
{
	char a[300];	
    cin.getline(a,300);
    int len=strlen(a);
    if(a[0]>='0'&&a[0]<='9')
     {
     	cout<<"no";
     	return 0;
	 }
    for(int i=0;i<len;i++)
    {
    	if(((a[i]>='0'&&a[i]<='9')||(a[i]>='A'&&a[i]<='Z')||(a[i]>='a'&&a[i]<='z')||a[i]=='_'))
    	{
    		;
		}
		else
		{
			cout<<"no";
			return 0;
		}
		
	}
	cout<<"yes";
	 return 0;
}