This Tutorial Explains C++ Character & Transformation Functions with Examples. Some Important Functions Covered are isdigit, islower, isupper, isalpha etc.:
In our previous tutorial on “library functions”, we saw the various headers that provide numerous functions that operate on different data types. The header <cctype.h> is one such header that contains a set of functions that classify and manipulate individual characters.
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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.
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.
In this tutorial, we will discuss the various character functions and see how each of these functions can be used in a program.
Table of Contents:
C++ Character Functions
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.
In the header <cctype.h>, we have two types of functions defined as stated below.
(i) Character Classification Functions
Character classification functions are used to check if the single character passed as an argument to the function belongs to a certain category.
We have tabularized the character classification functions included in <cctype.h> header below:
| No | Function name | Function Purpose |
|---|---|---|
| 1 | isalnum | Checks if a given character is alphanumeric |
| 2 | isalpha | Checks if the character is alphabetic |
| 3 | isblank | Checks if the character is blank |
| 4 | iscntrl | Checks if the given character is a control character |
| 5 | isdigit | Checks if the given character is a decimal digit |
| 6 | isgraph | Checks if the given character has a graphical representation |
| 7 | islower | Checks if a given character is lowercase |
| 8 | isprint | Checks if the character is a printable character |
| 9 | ispunct | Checks if the character is a punctuation character |
| 10 | isspace | Checks if the character is a white-space |
| 11 | isupper | Checks if the given character is uppercase |
| 12 | isxdigit | Checks if the character hexadecimal digit |
(ii) Character Transforming Functions
Character transforming functions convert between cases. The following functions are included in <cctype.h> file.
| No | Function Name | Function purpose |
|---|---|---|
| 1 | tolower | Converts uppercase character to lowercase |
| 2 | toupper | Converts lowercase character to uppercase |
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.
Isalnum
Function Prototype: int isalnum(int c);
Parameter(s): c=> A character which should be checked if alphanumeric or not
Return Value:
non-zero => c is alphanumeric
0 => c is not alphanumeric
Description: 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.
In C++, this function is locale-specific and its definition is present in header <locale>.
Example:
#include <iostream>
#include <cctype>
using namespace std;
int main()
{
char chary[12] = "Hello World";
// checking for isalnum() function
for (int i=0; i<12; i++)
{
if (isalnum(chary [i]))
cout << chary [i] << " is alphanumeric" << endl;
else
cout << chary [i] << " is not alphanumeric" << endl;
}
cout << endl;
}
Output:
Isalpha
Function Prototype: int isalpha(int c);
Parameter(s): c-> Character that is to be checked if alphabetic or not.
Return Value:
non-zero => c is alphabetic
0 => not alphabetic
Description: 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.
Example:
#include <iostream>
#include <cctype>
using namespace std;
int main()
{
char ch_alpha[5] = "sth1";
for (int i=0; i<5; i++) {
if (isalpha(ch_alpha[i]))
cout << ch_alpha[i] << " is an alphabet" << endl;
else
cout << ch_alpha[i] << " is not an alphabet" << endl;
}
cout << endl;
}
Output:
Isblank
Function Prototype: int isblank(int c);
Parameter(s): c=> Character which is to be checked.
Return Value:
non-zero => character is blank
0 => character is not blank
Description: 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.
In C++, the locale-specific version of isblank function exists in <locale>.
Example:
#include <iostream>
#include <cctype>
using namespace std;
int main()
{
char ch_alpha[6] = "s t h";
for (int i=0; i<6; i++)
{
if (isblank(ch_alpha[i]))
cout << ch_alpha[i] << " is a blank" << endl;
else
cout << ch_alpha[i] << " is not a blank" << endl;
}
cout << endl;
}
Output:
Note the last line in the output which says “ is not blank”. This is because of the character array’s last position that is not initialized to a value but still has a printing position. Hence it is not a blank.
Iscntrl
Function Prototype: int iscntrl(int c);
Parameter(s): c=> Character to be checked
Return Value:
non-zero=> c is control character
0=> c is not control character
Description: 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.
Example:
#include <iostream>
#include <cctype>
using namespace std;
int main()
{
char ch_alpha[6] = "s\nt\th";
for (int i=0; i<6; i++)
{
if (iscntrl(ch_alpha[i]))
cout << ch_alpha[i] << " is a control character" << endl;
else
cout << ch_alpha[i] << " is not a control character" << endl;
}
cout << endl;
}
Output:
Isdigit
Function Prototype: int isdigit(int c)
Parameter(s): c=> A character casted to int whose value is to be checked.
Return Value: non-zero => c is decimal digit
0=> c is not a digit
Description: 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.
Example:
#include <iostream>
#include <cctype>
using namespace std;
int main()
{
char ch_alpha[5] = "a12b";
for (int i=0; i<5; i++)
{
if (isdigit(ch_alpha[i]))
cout << ch_alpha[i] << " is a digit" << endl;
else
cout << ch_alpha[i] << " is not a digit" << endl;
}
cout << endl;
}
Output:
Isgraph
Function Prototype: int isgraph(int c)
Parameter(s): c=> Character casted int that is checked using the isgraph function
Return Value:
non-zero=> c is a graphical representation
0=> c is not a graphical representation
Description: 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.
Example:
#include <iostream>
#include <cctype>
using namespace std;
int main()
{
char ch_alpha[6] = "a~12b";
for (int i=0; i<6; i++)
{
if (isgraph(ch_alpha[i]))
cout << ch_alpha[i] << " is a graphical character" << endl;
else
cout << ch_alpha[i] << " is not a graphical character" << endl;
}
cout << endl;
}
Output:
Islower
Function Prototype: int islower(int c)
Parameter(s): c=> Character that is to be checked using the islower function.
Return Value:
non-zer0=> c is lowercase
0=> c is not lowercase
Description: The function islower checks if the given character c is lowercase or not.
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.
Example:
#include <iostream>
#include <cctype>
using namespace std;
int main()
{
char ch_alpha[4] = "Sth";
for (int i=0; i<4; i++)
{
if (islower(ch_alpha[i]))
cout << ch_alpha[i] << " is a lowercase character" << endl;
else
cout << ch_alpha[i] << " is not a lowercase character" << endl;
}
cout << endl;
}
Output:
Isprint
Function Prototype: int isprint(int c)
Parameter(s): c=> Character that is to be checked using isprint function.
Return Value:
non-zer0=> c is printable
0=> c is not printable
Description: Function isprint checks if the given character is printable. A printable character is the one that occupies a printing position in the display.
Example:
#include <iostream>
#include <cctype>
using namespace std;
int main()
{
char ch_alpha[4] = "Sth";
for (int i=0; i<4; i++)
{
if (isprint(ch_alpha[i]))
cout << ch_alpha[i] << " is a printable character" << endl;
else
cout << ch_alpha[i] << " is not a printable character" << endl;
}
cout << endl;
}
Output:
Ispunct
Function Prototype: int ispunct(int c)
Parameter(s): c=> Character that is to be checked using the ispunct function.
Return Value:
non-zer0=> c is a punctuation character
0=> c is not punctuation character
Description: 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.
Example:
#include <iostream>
#include <cctype>
using namespace std;
int main()
{
char ch_alpha[8] = "sth@123";
for (int i=0; i<8; i++)
{
if (ispunct(ch_alpha[i]))
cout << ch_alpha[i] << " is a punctuation character" << endl;
else
cout << ch_alpha[i] << " is not a punctuation character" << endl;
}
cout << endl;
}
Output:
Isspace
Function Prototype: int isspace(int c)
Parameter(s): c=> Character that is to be checked using the isspace function.
Return Value:
non-zer0=> c is a white-space
0=> c is not white-space
Description: This function checks if the given character is a white space. For the “C” locale, white-space characters are any of the following.
Example:
#include <iostream>
#include <cctype>
using namespace std;
int main()
{
char ch_alpha[7] = "s\tt\rh";
for (int i=0; i<7; i++)
{
if (isspace(ch_alpha[i]))
cout << ch_alpha[i] << " is a white space" << endl;
else
cout << ch_alpha[i] << " is not a white space" << endl;
}
cout << endl;
}
Output:
Isupper
Function Prototype: int isupper(int c)
Parameter(s): c=> Character that is to be checked using isupper function.
Return Value:
non-zer0=> c is uppercase
0=> c is not uppercase
Description: The functions islower checks if the given character c is uppercase or not.
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.
Example:
#include <iostream>
#include <cctype>
using namespace std;
int main()
{
char ch_alpha[4] = "STh";
for (int i=0; i<4; i++)
{
if (isupper(ch_alpha[i]))
cout << ch_alpha[i] << " is an uppercase character" << endl;
else
cout << ch_alpha[i] << " is not an uppercase character" << endl;
}
cout << endl;
}
Output:
Isxdigit
Function Prototype: int isxdigit(int c)
Parameter(s): c=> Character that is to be checked using isxdigit function.
Return Value:
non-zer0=> c is hexadecimal
0=> c is not a hexadecimal
Description: 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
Example:
#include <iostream>
#include <cctype>
using namespace std;
int main()
{
char ch_alpha[6] = "sbc10";
for (int i=0; i<6; i++)
{
if (isxdigit(ch_alpha[i]))
cout << ch_alpha[i] << " is hexadecimal digit" << endl;
else
cout << ch_alpha[i] << " is not hexadecimal digit" << endl;
}
cout << endl;
}
Output:
tolower
Function Prototype: int tolower(int c)
Parameter(s): c=> Character that is to be converted to lowercase.
Return Value:
returns the lower equivalent of c, unchanged otherwise.
The return value is int and can be implicitly cast to char.
Description: 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.
Example:
#include <iostream>
#include <cctype>
using namespace std;
int main()
{
char ch_alpha[4] = "STH";
cout<<ch_alpha<<" converted to lowercase:";
for (int i=0; i<4; i++)
{
cout<<(char)tolower(ch_alpha[i]);
}
cout << endl;
}
Output:
STH converted to lowercase:sth
toupper
Function Prototype: int toupper(int c)
Parameter(s): c=>character that is to be converted to uppercase
Return Value:
returns the upper equivalent of c, unchanged otherwise.
The return value is int and can be implicitly cast to char.
Description: 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.
Example:
#include <iostream>
#include <cctype>
using namespace std;
int main()
{
char ch_alpha[10] = "tutorials";
cout<<ch_alpha<<" converted to lowercase:";
for (int i=0; i<10; i++)
{
cout<<(char)toupper(ch_alpha[i]);
}
cout << endl;
}
Output:
tutorials converted to lowercase: TUTORIALS
Conclusion
This ends our tutorial on Character functions in C++.
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++.
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