Identification of Keyword or valid Identifier

22. Program to check whether the given string is a keyword or a valid identifier?

Program

#include<stdio.h>

#include<conio.h>

#include<string.h>

#include<ctype.h>

void main()

{

int i=0,flag=0;

char a[10][10]={"int","float","break","long","char","for","if","switch","else","while"},string[10];

clrscr();

printf("Enter a string :");

gets(string);

/*----Checking whether the string is in array a[][]----*/

for(i=0;i<10;i++)      

{

if((strcmp(a[i],string)==0))

flag=1;

}

/*----If it is in the array then it is a keyword----*/

if(flag==1)

printf("\n%s is a keyword ",string);

/*----Otherwise check whether the string is an identifier----*/

else

{

flag=0;
/*----Checking the 1^st character*----*/

if((string[0]=='_')||(isalpha(string[0])!=0))

{
/*---Checking rest of the characters*---*/

for(i=1;string[i]!='\0';i++)

if((isalnum(string[i])==0)&&(string[i]!='_'))

flag=1;

}

else

flag=1;

if( flag==0)

printf("\n%s is an identifier ",string);

else

printf("\n%s is neither a keyword nor an identifier ",string);

}

getch();

}

*Note: An identifier must start with an underscore(‘_’) or an alphabet.
            An identifier must contain only alphabets, numbers or ‘_’ after the first character.

Output

Enter a string :int

int is a keyword

Enter a string :abc

abc is an identifier

Enter a string :123abc

123abc is neither a keyword nor an identifier