Character Classification in C++ : cctype

Character classification in C++ is possible using functions specified in function library. These functions are included in the <cctype> header file.

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

Syntax:

int isalpha ( char c );

Example:

C++

// C++ program to demonstrate isalpha()
#include <cctype>
#include <iostream>
using namespace std;

// Driver Code
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;
    }
}

Output

g is alphabet
1 is not alphabet

There comes two functions in the alphabet .

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

Syntax:

int isupper(char c);

Example:

C++

// C++ program to demonstrate isalpha()
#include <cctype>
#include <iostream>
using namespace std;

// Driver Code
int main()
{
    // initializing character array
    char ch[5] = "Gg";

    // checking for isupper() function
    for (int i = 0; i < 2; i++) {
        if (isupper(ch[i]))
            cout << ch[i] << " is an upper  alphabet" << endl;
        else
            cout << ch[i] << " is not an upper alphabet" << endl;
    }
}

Output

G is an upper  alphabet
g is not an upper alphabet

b. islower(): This function returns true if the character is a lower alphabet else returns false. All the characters from a-z return true according to this function.

Syntax:

int islower(char c);

C++

// C++ program to demonstrate isalpha()
#include <cctype>
#include <iostream>
using namespace std;

// Driver Code
int main()
{
    // initializing character array
    char ch[5] = "Gg";

    // checking for islower() function
    for (int i = 0; i < 2; i++) {
        if (islower(ch[i]))
            cout << ch[i] << " is an lower  alphabet" << endl;
        else
            cout << ch[i] << " is not an lower alphabet" << endl;
    }
}

Output

G is not an lower alphabet
g is an lower  alphabet

2. isalnum(): This function returns true if the 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.

Syntax:

int isalnum ( char c );

Example:

C++

// C++ program to demonstrate isalnum()
#include <cctype>
#include <iostream>
using namespace std;

// Driver Code
int main()
{
    // initializing character array
    char ch[5] = "g1";

    // 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;
    }
}

Output

g is alphanumeric
1 is alphanumeric

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

Syntax:

int isdigit ( char c );

Example:

CPP

// C++ program to demonstrate isdigit()
#include <cctype>
#include <iostream>
using namespace std;

int main()
{
    // initializing character array
    char ch[5] = "g1";

    // 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 not digit
1 is digit

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

Syntax:

int isblank ( char c );

Example:

C++

// C++ program to demonstrate isblank()
#include <cctype>
#include <iostream>
using namespace std;

// Driver Code
int main()
{
    // initializing character array
    char ch[4] = " \n\t";

    // 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;
    }
}

Output

 Character is blank
 Character is not blank
 Character is blank

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

Syntax:

int isspace ( char c );

Example:

C++

// C++ program to demonstrate isspace()
#include <cctype>
#include <iostream>
using namespace std;

// Driver Code
int main()
{
    // initializing character array
    char ch[4] = " \n\t";

    // 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 space
 Character is space
 Character is space

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

Syntax:

int iscntrl ( char c );

Example:

CPP

// C++ program to demonstrate iscntrl()
#include <cctype>
#include <iostream>
using namespace std;

// Driver Code
int main()
{
    // initializing character array
    char ch[4] = " \n\t";

    // 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;
    }
}

Output

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

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

Syntax:

int isprint ( char c );

Example:

C++

// C++ program to demonstrate isprint()
#include <cctype>
#include <iostream>
using namespace std;

// Driver Code
int main()
{
    // initializing character array
    char ch[6] = "\t@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;
    }
}

Output

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

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

Syntax:

int isxdigit ( char c );

Example:

C++

// C++ program to demonstrate isxdigit()
#include <cctype>
#include <iostream>
using namespace std;

// Driver Code
int main()
{
    // initializing character array
    char ch[6] = "\t@gf1";

    // 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;
    }
}

Output

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

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

Syntax:

int ispunct ( char c );

Example:

CPP

// C++ program to demonstrate ispunct()
#include <cctype>
#include <iostream>
using namespace std;

// Driver Code
int main()
{
    // initializing character array
    char ch[6] = "\t@gf1";

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