{"id":104374,"date":"2020-02-27T10:21:00","date_gmt":"2020-02-27T10:21:00","guid":{"rendered":"https:\/\/www.softwaretestinghelp.com\/?page_id=104374"},"modified":"2025-04-01T08:13:38","modified_gmt":"2025-04-01T08:13:38","slug":"cpp-character-functions","status":"publish","type":"page","link":"https:\/\/www.softwaretestinghelp.com\/cpp-character-functions\/","title":{"rendered":"C++ Character Classification And Tranformation Functions"},"content":{"rendered":"

This Tutorial Explains C++ Character & Transformation Functions with Examples. Some Important Functions Covered are isdigit, islower, isupper, isalpha etc.:<\/strong><\/p>\n

In our previous tutorial on \u201clibrary functions\u201d, we saw the various headers that provide numerous functions that operate on different data types. The header <cctype.h><\/strong> is one such header that contains a set of functions that classify and manipulate individual characters.<\/p>\n

=> Visit Here To Learn C++ From Scratch.<\/a><\/strong><\/p>\n

<\/strong><\/em><\/p>\n

The functions declared in <cctype.h> header, take a single character (int equivalent) as a parameter and return an integer value that can either be a Boolean value or a character value. A value 0 (zero) indicates false while a value other than 0 (non-zero) indicates true.<\/p>\n

\"C++<\/a><\/p>\n

These single character functions can be used in the program by including the header <cctype.h>. These functions are widely used and accepted and are extremely useful in C++ programming for testing and transforming or manipulating characters.<\/p>\n

In this tutorial, we will discuss the various character functions and see how each of these functions can be used in a program.<\/p>\n

C++ Character Functions<\/h2>\n

C++ character functions are the functions that take only a single character as a parameter (casted to int) and return a result. These can be classification functions like isalpha, isalnum, isdigit, islower, isupper, etc. to name a few and transforming functions like toupper and tolower that transform a given character into uppercase or lowercase respectively.<\/strong><\/p>\n

In the header <cctype.h>, we have two types of functions defined as stated below.<\/p>\n

(i) Character Classification Functions<\/strong><\/span><\/p>\n

Character classification functions are used to check if the single character passed as an argument to the function belongs to a certain category.<\/p>\n

We have tabularized the character classification functions included in <cctype.h> header below:<\/strong><\/p>\n\n

\n\n\n\n\t\n\n\t\n\t\n\t\n\t\n\t\n\t\n\t\n\t\n\t\n\t\n\t\n\t
No<\/th>Function name<\/th>Function Purpose<\/th>\n<\/tr>\n<\/thead>\n
1<\/td>isalnum<\/td>Checks if a given character is alphanumeric<\/td>\n<\/tr>\n
2<\/td>isalpha<\/td>Checks if the character is alphabetic<\/td>\n<\/tr>\n
3<\/td>isblank<\/td>Checks if the character is blank<\/td>\n<\/tr>\n
4<\/td>iscntrl<\/td>Checks if the given character is a control character<\/td>\n<\/tr>\n
5<\/td>isdigit<\/td>Checks if the given character is a decimal digit<\/td>\n<\/tr>\n
6<\/td>isgraph<\/td>Checks if the given character has a graphical representation<\/td>\n<\/tr>\n
7<\/td>islower<\/td>Checks if a given character is lowercase<\/td>\n<\/tr>\n
8<\/td>isprint<\/td>Checks if the character is a printable character<\/td>\n<\/tr>\n
9<\/td>ispunct<\/td>Checks if the character is a punctuation character<\/td>\n<\/tr>\n
10<\/td>isspace<\/td>Checks if the character is a white-space<\/td>\n<\/tr>\n
11<\/td>isupper<\/td>Checks if the given character is uppercase<\/td>\n<\/tr>\n
12<\/td>isxdigit<\/td>Checks if the character hexadecimal digit<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n\n

(ii) Character Transforming Functions<\/strong><\/span><\/p>\n

Character transforming functions convert between cases. The following functions are included in <cctype.h> file.<\/strong><\/p>\n\n

\n\n\n\n\t\n\n\t\n\t
No<\/th>Function Name<\/th>Function purpose<\/th>\n<\/tr>\n<\/thead>\n
1<\/td>tolower<\/td>Converts uppercase character to lowercase <\/td>\n<\/tr>\n
2<\/td>toupper<\/td>Converts lowercase character to uppercase <\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n\n

Let’s see each of the character functions (classification and transforming) in detail. We will also present a simple C++ programming example for each of the functions.<\/p>\n

Isalnum<\/span><\/h3>\n

Function Prototype: <\/strong>int isalnum(int c);<\/p>\n

Parameter(s): <\/strong>c=> A character which should be checked if alphanumeric or not<\/p>\n

Return Value: <\/strong><\/p>\n

non-zero => c is alphanumeric<\/p>\n

0 => c is not alphanumeric<\/p>\n

Description: <\/strong>This function checks if a given character c is alphanumeric or not. By alphanumeric, it means a character is between A(a)-Z(z) or 0 to 9.<\/p>\n

In C++, this function is locale-specific and its definition is present in header <locale>.<\/p>\n

Example:<\/strong><\/span><\/p>\n

#include <iostream>\r\n#include <cctype>\r\nusing namespace std;\r\nint main()\r\n{\r\n   char chary[12] = "Hello World"; \r\n  \r\n    \/\/ checking for isalnum() function \r\n    for (int i=0; i<12; i++) \r\n    { \r\n        if (isalnum(chary [i])) \r\n            cout << chary [i] << " is alphanumeric" << endl; \r\n        else\r\n            cout << chary [i]  << " is not alphanumeric" << endl; \r\n    } \r\n   cout << endl; \r\n} <\/pre>\n
Output:<\/strong><\/p>\n
\"Isalnum<\/a><\/p>\n
Isalpha<\/span><\/h3>\n
 Function Prototype: <\/strong>int isalpha(int c);<\/p>\n
 Parameter(s): <\/strong>c-> Character that is to be checked if alphabetic or not.<\/p>\n
 Return Value:<\/strong><\/p>\n
non-zero => c is alphabetic<\/p>\n
0 => not alphabetic<\/p>\n
 Description: <\/strong>This function checks if a given character c is alphabetic character i.e. among lowercase and uppercase letters. Like isalnum this function also depends on the locale that we are using.<\/p>\n
 Example:<\/strong><\/span><\/p>\n
#include <iostream>\r\n#include <cctype>\r\nusing namespace std;\r\nint main()\r\n{\r\n    char ch_alpha[5] = "sth1"; \r\n    for (int i=0; i<5; i++) { \r\n        if (isalpha(ch_alpha[i])) \r\n            cout << ch_alpha[i] << " is an alphabet" << endl; \r\n        else\r\n            cout << ch_alpha[i] << " is not an alphabet" << endl; \r\n    } \r\n    cout << endl; \r\n}<\/pre>\n
Output:<\/strong><\/p>\n
\"Isalpha<\/a><\/p>\n
Isblank<\/span><\/h3>\n
 Function Prototype: <\/strong>int isblank(int c);<\/p>\n
 Parameter(s): <\/strong>c=> Character which is to be checked.<\/p>\n
 Return Value:<\/strong><\/p>\n
non-zero => character is blank<\/p>\n
0 => character is not blank<\/p>\n
 Description: <\/strong>This function checks if the given character is a blank or not. Blank character is a space character that is used to separate words in a line of text.<\/p>\n
In C++, the locale-specific version of isblank function exists in <locale>.<\/p>\n
 Example:<\/strong><\/span><\/p>\n
#include <iostream>\r\n#include <cctype>\r\nusing namespace std;\r\nint main()\r\n{\r\n    char ch_alpha[6] = "s t h"; \r\n  \r\n    for (int i=0; i<6; i++) \r\n    { \r\n        if (isblank(ch_alpha[i])) \r\n            cout << ch_alpha[i] << " is a blank" << endl; \r\n        else\r\n            cout << ch_alpha[i] << " is not a blank" << endl; \r\n    } \r\n    cout << endl; \r\n}<\/pre>\n
Output:<\/strong><\/p>\n
\"Isblank<\/a><\/p>\n
Note the last line in the output which says \u201c is not blank\u201d. This is because of the character array\u2019s last position that is not initialized to a value but still has a printing position. Hence it is not a blank.<\/p>\n
Iscntrl<\/span><\/h3>\n
 Function Prototype:<\/strong> int iscntrl(int c);<\/p>\n
 Parameter(s): <\/strong>c=> Character to be checked<\/p>\n
 Return Value:<\/strong><\/p>\n
non-zero=> c is control character<\/p>\n
0=> c is not control character<\/p>\n
 Description: <\/strong>Function checks if the given parameter is a control character. A control character is a character that does not appear in the display or does not occupy a printing position.<\/p>\n
 Example:<\/strong><\/span><\/p>\n
#include <iostream>\r\n#include <cctype>\r\nusing namespace std;\r\nint main()\r\n{\r\n    char ch_alpha[6] = "s\\nt\\th"; \r\n  \r\n    for (int i=0; i<6; i++) \r\n    { \r\n        if (iscntrl(ch_alpha[i])) \r\n            cout << ch_alpha[i] << " is a control character" << endl; \r\n        else\r\n            cout << ch_alpha[i] << " is not a control character" << endl; \r\n    } \r\n    cout << endl; \r\n}<\/pre>\n
 Output:<\/strong><\/p>\n
\"Iscntrl\"<\/a><\/p>\n
Isdigit<\/span><\/h3>\n
 Function Prototype:<\/strong> int isdigit(int c)<\/p>\n
 Parameter(s): <\/strong>c=> A character casted to int whose value is to be checked.<\/p>\n
 Return Value:<\/strong> non-zero => c is decimal digit<\/p>\n
0=> c is not a digit<\/p>\n
 Description: <\/strong>This function checks if the given parameter is a decimal digit or not. A character is a decimal digit if its value is between 0 and 9.<\/p>\n
 Example:<\/strong><\/span><\/p>\n
#include <iostream>\r\n#include <cctype>\r\nusing namespace std;\r\nint main()\r\n{\r\n    char ch_alpha[5] = "a12b"; \r\n  \r\n    for (int i=0; i<5; i++) \r\n    { \r\n        if (isdigit(ch_alpha[i])) \r\n            cout << ch_alpha[i] << " is a digit" << endl; \r\n        else\r\n            cout << ch_alpha[i] << " is not a digit" << endl; \r\n    } \r\n    cout << endl; \r\n}<\/pre>\n
Output:<\/strong><\/p>\n
\"Isdigit\"<\/a><\/p>\n
Isgraph<\/span><\/h3>\n
 Function Prototype: <\/strong>int isgraph(int c)<\/p>\n
 Parameter(s): <\/strong>c=> Character casted int that is checked using the isgraph function<\/p>\n
 Return Value: <\/strong><\/p>\n
non-zero=> c is a graphical representation<\/p>\n
0=> c is not a graphical representation<\/p>\n
 Description: <\/strong>Function checks if the given character c is a character with graphical representation. A character that can be printed is a character with graphical representation.<\/p>\n
 Example:<\/strong><\/span><\/p>\n
#include <iostream>\r\n#include <cctype>\r\nusing namespace std;\r\nint main()\r\n{\r\n    char ch_alpha[6] = "a~12b"; \r\n  \r\n    for (int i=0; i<6; i++) \r\n    { \r\n        if (isgraph(ch_alpha[i])) \r\n            cout << ch_alpha[i] << " is a graphical character" << endl; \r\n        else\r\n            cout << ch_alpha[i] << " is not a graphical character" << endl; \r\n    } \r\n    cout << endl; \r\n}<\/pre>\n
Output:<\/strong><\/p>\n
\"Isgraph\"<\/a><\/p>\n
Islower<\/span><\/h3>\n
 Function Prototype:<\/strong> int islower(int c)<\/p>\n
 Parameter(s): <\/strong>c=> Character that is to be checked using the islower function.<\/p>\n
 Return Value:<\/strong><\/p>\n
non-zer0=> c is lowercase<\/p>\n
0=> c is not lowercase<\/p>\n
 Description: <\/strong>The function islower checks if the given character c is lowercase or not.<\/p>\n
A lowercase character is the one that has one of the values: a b c d e f g h I j k l m n o p q r s t u v w x y z.<\/p>\n
 Example:<\/strong><\/span><\/p>\n
#include <iostream>\r\n#include <cctype>\r\nusing namespace std;\r\nint main()\r\n{\r\n    char ch_alpha[4] = "Sth"; \r\n  \r\n    for (int i=0; i<4; i++) \r\n    { \r\n        if (islower(ch_alpha[i])) \r\n            cout << ch_alpha[i] << " is a lowercase character" << endl; \r\n        else\r\n            cout << ch_alpha[i] << " is not a lowercase character" << endl; \r\n    } \r\n    cout << endl; \r\n}<\/pre>\n
Output:<\/strong><\/p>\n
\"Islower\"<\/a><\/p>\n
Isprint<\/span><\/h3>\n
 Function Prototype:<\/strong> int isprint(int c)<\/p>\n
 Parameter(s):<\/strong> c=> Character that is to be checked using isprint function.<\/p>\n
 Return Value:<\/strong><\/p>\n
non-zer0=> c is printable<\/p>\n
0=> c is not printable<\/p>\n
 Description: <\/strong>Function isprint checks if the given character is printable. A printable character is the one that occupies a printing position in the display.<\/p>\n
 Example:<\/strong><\/span><\/p>\n
#include <iostream>\r\n#include <cctype>\r\nusing namespace std;\r\nint main()\r\n{\r\n    char ch_alpha[4] = "Sth"; \r\n  \r\n    for (int i=0; i<4; i++) \r\n    { \r\n        if (isprint(ch_alpha[i])) \r\n            cout << ch_alpha[i] << " is a printable character" << endl; \r\n        else\r\n            cout << ch_alpha[i] << " is not a printable character" << endl; \r\n    } \r\n    cout << endl; \r\n}<\/pre>\n
Output:<\/strong><\/p>\n
\"Isprint\"<\/a><\/p>\n
Ispunct<\/span><\/h3>\n
 Function Prototype:<\/strong> int ispunct(int c)<\/p>\n
 Parameter(s):<\/strong> c=> Character that is to be checked using the ispunct function.<\/p>\n
 Return Value:<\/strong><\/p>\n
non-zer0=> c is a punctuation character<\/p>\n
0=> c is not punctuation character<\/p>\n
 Description: <\/strong>This function checks if the given character is a punctuation character. A character that is a graphical character (from isgraph) and not an alphanumeric (from isalnum) is said to be a punctuation character.<\/p>\n
 Example:<\/strong><\/span><\/p>\n
#include <iostream>\r\n#include <cctype>\r\nusing namespace std;\r\nint main()\r\n{\r\n    char ch_alpha[8] = "sth@123"; \r\n  \r\n    for (int i=0; i<8; i++) \r\n    { \r\n        if (ispunct(ch_alpha[i])) \r\n            cout << ch_alpha[i] << " is a punctuation character" << endl; \r\n        else\r\n            cout << ch_alpha[i] << " is not a punctuation character" << endl; \r\n    } \r\n    cout << endl; \r\n}<\/pre>\n
Output:<\/strong><\/p>\n
\"Ispunct\"<\/a><\/p>\n
Isspace<\/span><\/h3>\n
 Function Prototype:<\/strong> int isspace(int c)<\/p>\n
 Parameter(s):<\/strong> c=> Character that is to be checked using the isspace function.<\/p>\n
 Return Value:<\/strong><\/p>\n
non-zer0=> c is a white-space<\/p>\n
0=> c is not white-space<\/p>\n
 Description:<\/strong> This function checks if the given character is a white space. For the \u201cC\u201d locale, white-space characters are any of the following.<\/p>\n
 Example:<\/strong><\/span><\/p>\n
#include <iostream>\r\n#include <cctype>\r\nusing namespace std;\r\nint main()\r\n{\r\n    char ch_alpha[7] = "s\\tt\\rh"; \r\n  \r\n    for (int i=0; i<7; i++) \r\n    { \r\n        if (isspace(ch_alpha[i])) \r\n            cout << ch_alpha[i] << " is a white space" << endl; \r\n        else\r\n            cout << ch_alpha[i] << " is not a white space" << endl; \r\n    } \r\n    cout << endl; \r\n}<\/pre>\n
 Output:<\/strong><\/p>\n
\"Isspace\"<\/a><\/p>\n
Isupper<\/span><\/h3>\n
 Function Prototype:<\/strong> int isupper(int c)<\/p>\n
 Parameter(s):<\/strong> c=> Character that is to be checked using isupper function.<\/p>\n
 Return Value:<\/strong><\/p>\n
non-zer0=> c is uppercase<\/p>\n
0=> c is not uppercase<\/p>\n
 Description:<\/strong> The functions islower checks if the given character c is uppercase or not.<\/p>\n
An uppercase character is the one that has one of the values: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z.<\/p>\n
 Example:<\/strong><\/span><\/p>\n
#include <iostream>\r\n#include <cctype>\r\nusing namespace std;\r\nint main()\r\n{\r\n    char ch_alpha[4] = "STh"; \r\n  \r\n    for (int i=0; i<4; i++) \r\n    { \r\n        if (isupper(ch_alpha[i])) \r\n            cout << ch_alpha[i] << " is an uppercase character" << endl; \r\n        else\r\n            cout << ch_alpha[i] << " is not an uppercase character" << endl; \r\n    } \r\n    cout << endl; \r\n}<\/pre>\n
 Output:<\/strong><\/p>\n
\"Isupper\"<\/a><\/p>\n
Isxdigit<\/span><\/h3>\n
Function Prototype:<\/strong> int isxdigit(int c)<\/p>\n
 Parameter(s):<\/strong> c=> Character that is to be checked using isxdigit function.<\/p>\n
 Return Value:<\/strong><\/p>\n
non-zer0=> c is hexadecimal<\/p>\n
0=> c is not a hexadecimal<\/p>\n
 Description: <\/strong>This function checks if the given character is a hexadecimal digit. Valid hexadecimal digits are 0 1 2 3 4 5 6 7 8 9 a b c d e f A B C D E F<\/p>\n
 Example:<\/strong><\/span><\/p>\n
#include <iostream>\r\n#include <cctype>\r\nusing namespace std;\r\nint main()\r\n{\r\n    char ch_alpha[6] = "sbc10"; \r\n  \r\n    for (int i=0; i<6; i++) \r\n    { \r\n        if (isxdigit(ch_alpha[i])) \r\n            cout << ch_alpha[i] << " is hexadecimal digit" << endl; \r\n        else\r\n            cout << ch_alpha[i] << " is not hexadecimal digit" << endl; \r\n    } \r\n    cout << endl; \r\n}<\/pre>\n
 Output:<\/strong><\/p>\n
\"Isxdigit\"<\/a><\/p>\n
tolower<\/span><\/h3>\n
 Function Prototype: <\/strong>int tolower(int c)<\/p>\n
 Parameter(s): <\/strong>c=> Character that is to be converted to lowercase.<\/p>\n
 Return Value: <\/strong><\/p>\n
returns the lower equivalent of c, unchanged otherwise.<\/p>\n
The return value is int and can be implicitly cast to char.<\/p>\n
 Description: <\/strong>This converts the given character c into its lowercase equivalent. If the conversion is not possible for a given character, then the unchanged value (c) is returned.<\/p>\n
 Example:<\/strong><\/span><\/p>\n
#include <iostream>\r\n#include <cctype>\r\nusing namespace std;\r\nint main()\r\n{\r\n    char ch_alpha[4] = "STH"; \r\n  \r\n    cout<<ch_alpha<<" converted to lowercase:";\r\n    for (int i=0; i<4; i++) \r\n    { \r\n        cout<<(char)tolower(ch_alpha[i]);\r\n    } \r\n    cout << endl; \r\n}<\/pre>\n
 Output:<\/strong><\/p>\n
STH\u00a0converted\u00a0to\u00a0lowercase:sth<\/p>\n
toupper<\/span><\/h3>\n
 Function Prototype:<\/strong> int toupper(int c)<\/p>\n
 Parameter(s): <\/strong>c=>character that is to be converted to uppercase<\/p>\n
 Return Value:<\/strong><\/p>\n
returns the upper equivalent of c, unchanged otherwise.<\/p>\n
The return value is int and can be implicitly cast to char.<\/p>\n
 Description:<\/strong> This converts the given character c into its uppercase equivalent. If a conversion is not possible for a given character, then the unchanged value (c) is returned.<\/p>\n
 Example:<\/strong><\/span><\/p>\n
#include <iostream>\r\n#include <cctype>\r\nusing namespace std;\r\nint main()\r\n{\r\n    char ch_alpha[10] = "tutorials"; \r\n  \r\n    cout<<ch_alpha<<" converted to lowercase:";\r\n    for (int i=0; i<10; i++) \r\n    { \r\n        cout<<(char)toupper(ch_alpha[i]);\r\n    } \r\n    cout << endl; \r\n}<\/pre>\n
 Output:<\/em><\/strong><\/p>\n
tutorials converted to lowercase: TUTORIALS<\/p>\n
Conclusion<\/h2>\n
This ends our tutorial on Character functions in C++.<\/p>\n
In this tutorial, we have seen various functions that take a single character and then either classify them or convert them. In our subsequent tutorials, we will discuss string and their functions and classes related to C++.<\/p>\n
=> Discover The Simple C++ Training Series Here.<\/a><\/strong><\/p>\n\r\n\t\t\t
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