LOGIC:
Read the given input string.Check the initial character of the string is numerical or any special character except ‘_’ then print it is not a valid identifier.Otherwise print it as valid identifier if remaining characters of string doesn’t contains any special characters except ‘_’.
PROGRAM: #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(); }
OUTPUT: Enter an identifier: first Valid identifier Enter an identifier:1aqw Not a valid identifier