Character Classification in C++ : cctype

Character classification in C++ is possible using functions specified in function library . Numerous function to classify characters are discussed in this article.

1. isalpha() : This function returns true if character is an alphabet else returns false. All the characters from a-z and A-Z return true according to this function.

2. isalnum() : This function returns true if character is an alphabet or a number else returns false. All the characters from a-z , A-Z and all numbers return true according to this function.

3. isdigit() : This function returns true if character is a number else returns false. All all numbers return true according to this function.

// C++ program to demonstrate insalpha(), isnum()  
// and isdigit() 
#include <cctype> 
#include <iostream> 
using namespace std; 
  
int main() 
{ 
    // initializing character array 
    char ch[5] = "g1"; 
  
    // checking for isalpha() function 
    for (int i=0; i<2; i++) 
    { 
        if (isalpha(ch[i])) 
            cout << ch[i] << " is alphabet" << endl; 
        else
            cout << ch[i] << " is not alphabet" << endl; 
    } 
  
    cout << endl; 
  
    // checking for isalnum() function 
    for (int i=0; i<2; i++) 
    { 
        if (isalnum(ch[i])) 
            cout << ch[i] << " is alphanumeric" << endl; 
        else
            cout << ch[i]  << " is not alphanumeric" << endl; 
    } 
  
    cout << endl; 
  
    // checking for isdigit() function 
    for (int i=0; i<2; i++) 
    { 
        if (isdigit(ch[i])) 
            cout << ch[i]  <<  " is digit" << endl; 
        else
            cout << ch[i] << " is not digit" << endl; 
    } 
} 

Output :

g is alphabet
1 is not alphabet

g is alphanumeric
1 is alphanumeric

g is not digit
1 is digit

4. isblank() : This function returns true if character is a space or tab else returns false.

5. isspace() : This function returns true if character is a space or tab or whitespace control code ( Eg. , ) else returns false.

6. iscntrl() : This function returns true if character is tab or any control code else returns false.

// C++ program to demonstrate iscntrl(), isblank() and 
// isspace() 
#include <cctype> 
#include <iostream> 
using namespace std; 
  
int main() 
{ 
    // initializing character array 
    char ch[4] = "
"; 
  
    // checking for iscntrl() function 
    for (int i=0; i<3; i++) 
    { 
        if (iscntrl(ch[i])) 
            cout << " Character is control code " << endl; 
        else
            cout << " Character is not control code" << endl; 
    } 
  
    cout << endl; 
  
    // checking for isblank() function 
    for (int i=0; i<3; i++) 
    { 
        if (isblank(ch[i])) 
            cout << " Character is blank" << endl; 
        else
            cout << " Character is not blank" << endl; 
    } 
  
    cout << endl; 
  
    // checking for isspace() function 
    for (int i=0; i<3; i++) 
    { 
        if (isspace(ch[i])) 
            cout << " Character is space" << endl; 
        else
            cout << " Character is not space" << endl; 
    } 
} 

Output :

 Character is not control code
 Character is control code 
 Character is control code 

 Character is blank
 Character is not blank
 Character is blank

 Character is space
 Character is space
 Character is space

7. isprint() : This function returns true if character is printable on console i.e. all characters except control code else returns false.

8. isxdigit() : This function returns true if character is hexadecimal i.e 0-9 and a-f else returns false.

9. ispunct() : This function returns true if character is punctuation mark else returns false.

// C++ program to demonstrate isprint(), isxdigit() and 
// ispunct() 
#include <cctype> 
#include <iostream> 
using namespace std; 
  
int main() 
{ 
    // initializing character array 
    char ch[6] = "	@gf1"; 
  
    // checking for isprint() function 
    for (int i=0; i<5; i++) 
    { 
        if (isprint(ch[i])) 
            cout << ch[i] << " is printable character " << endl; 
        else
            cout << ch[i] << " is not printable Character" << endl; 
    } 
  
    cout << endl; 
  
    // checking for isxdigit() function 
    for (int i=0; i<5; i++) 
    { 
        if (isxdigit(ch[i])) 
            cout << ch[i] << " is hexadecimal Character" << endl; 
        else
            cout << ch[i] << " is not hexadecimal Character" << endl; 
    } 
  
    cout << endl; 
  
    // checking for ispunct() function 
    for (int i=0; i<5; i++) 
    { 
        if (ispunct(ch[i])) 
            cout << ch[i] << "  is punctuation mark" << endl; 
        else
            cout << ch[i] <<  "  is not punctuation mark" << endl; 
    } 
} 

Output :

	 is not printable Character
@ is printable character 
g is printable character 
f is printable character 
1 is printable character 

	 is not hexadecimal Character
@ is not hexadecimal Character
g is not hexadecimal Character
f is hexadecimal Character
1 is hexadecimal Character

	  is not punctuation mark
@  is punctuation mark
g  is not punctuation mark
f  is not punctuation mark
1  is not punctuation mark

Reference : http://www.cplusplus.com/reference/cctype/

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Character Classification in C++ : cctype

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