Write a C program to test whether a given identifier is valid or not

#include<stdio.h>
#include<conio.h>
#include<ctype.h>
void main()
{
    char a[10];
    int flag,
    i=1;
    clrscr();
    printf("\n Enter an identifier:");
    gets(a);
    if(isalpha(a[0]))
    flag=1;
    else
    printf("\n Not a valid identifier");
    while(a[i]!='\0')
    {
        if(!isdigit(a[i])&&!isalpha(a[i]))
        {
            flag=0; break;
           
        } i++;
       
    }
    if(flag==1)
    printf("\n Valid identifier");
    getch();
   
}