Character Classification in C++ : cctype - GeeksforGeeks

08 Mar, 2022
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 Codeint 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;    }}
g is alphabet
1 is not 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 Codeint 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;    }}
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;    }}
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 Codeint 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;    }}
 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 Codeint 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;    }}
 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 Codeint 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;    }}
 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 Codeint 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;    }}
     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 Codeint 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;    }}
     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 Codeint 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;    }}
     is not punctuation mark
@ is punctuation mark
g is not punctuation mark
f is not punctuation mark
1 is not punctuation mark
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