How to check if a string is a valid identifier or not in C++?
By Brijesh KumarIn this tutorial, we will learn how we can check if a string is a valid identifier or not in C++ programming. We are going to see it with an example code snippet. So stay here and keep reading this article…
Now to check whether a string is a valid identifier or not in C++. First, let us understand what is a valid identifier in C++.
A string can be a valid identifier if it’s initial(first) letter is either an underscore(_) or lowercase alphabet(‘a’-‘z’) or uppercase alphabet(‘A’-‘Z’). Followed by after initial letter, all the next letters can be a combination of either digit(‘0’-‘9’), lowercase alphabets(‘a’-‘z’), uppercase alphabets(‘A’-‘Z’) or underscore(_).
Above all, the letters followed by an initial letter should not have any spaces( ) and the special symbols($,&,@.^, etc).
Now let us understand it more clearly with a program.
//illustrating how to check whether
//a string is valid identifier or not.
#include <bits/stdc++.h>
using namespace std;
int main()
{
string s;
int c=0,flagv;
cout<<"enter any string: ";
cin>>s; //input any string
//check whether it is a valid identifier or not
if( (s[0]>='a'&&s[0]<='z')
||
(s[0]>='A'&&s[0]<='Z')
||
(s[0]=='_') )
{
for(int i=1;i<s.length();i++)
{
if((s[i]>='a'&& s[i]<='z')
||
(s[i]>='A' && s[i]<='Z')
||
(s[i]>='0'&& s[i]<='9')
||
(s[i]=='_') )
{
c++;
} }
if(c==s.length())
{
flagv=0;
}
}
else
{
flagv=1;
}
//if flagv=1 then string is not a valid identifier
if(flagv==1)
cout<<s<<"is not valid identifier";
//otherwise string is a valid identifier
else
cout<<s<<" is valid identifier";
return 0;
}Read the comments in the program above for better understanding.
The above code displays the following output i.e., either string is a valid identifier or not a valid identifier.
Some of the valid identifiers are,
1. enter any string: abc_ abc_ is valid identifier. 2. enter any string: Amc876_d Amc876_d is valid identifier. 3. enter any string: _hi777 _hi777 is valid identifier.
Some of the string which is not valid identifiers are as shown below,
1. enter any string: %defA_c %defA_c is not valid identifier. 2. enter any string: %@^9_8 %@^9_8 is not valid identifier.
Recommended articles:
Random Alphanumeric String Generation in C++
Python program to check if a string is a valid identifier or not
there is error .if i give space any letter it show valid but it’s false and so many error!