This post contains a list of predefined functions defined in ctype.h which we can use on an individual C character. You can learn more about C string from our C course.
The functions present in the ctpye.h header are:
| Function | Use |
|---|---|
| isalnum | checks if a character is an alphanumeric |
| isalpha | checks if a character is an alphabet |
| iscntrl | checks if a character is control character |
| isdigit | checks if a character is digit |
| isgraph | checks if a character is graphical representation |
| islower | checks if a character is lowercase |
| isprint | checks if a character is printable |
| ispunct | checks if a character is punctuation |
| issapce | checks if a charater is white-space |
| isupper | checks if a charater is uppercase |
| isxdigit | checks if a character is hexadecimal digit |
| tolower | converts character to lowercase |
| toupper | converts character to uppercase |
isalnum
isalnum(x) will be true when x is an alphabet or a digit.
#include <stdio.h>
#include <ctype.h>
int main()
{
char s[] = "123abc!@#";
int i = 0;
while(s[i] != '\0')
{
if(isalnum(s[i]))
printf("%c is alphanumeric\n",s[i]);
else
printf("%c is NOT alphanumeric\n",s[i]);
i++;
}
return 0;
}
Output
1 is alphanumeric
2 is alphanumeric
3 is alphanumeric
a is alphanumeric
b is alphanumeric
c is alphanumeric
! is NOT alphanumeric
@ is NOT alphanumeric
# is NOT alphanumeric
Please note that the parameter of the function ‘alnum’ is an int i.e., int alnum(int c) and it just typecasts other data types to int. For example, we passed a char in the above examples and then it was typecasted to int.
isalpha
int isalpha(int c)
isaplha(x) will be true when x is an alphabet.
#include <stdio.h>
#include <ctype.h>
int main()
{
char s[] = "123abc!@#";
int i = 0;
while(s[i] != '\0')
{
if(isalpha(s[i]))
printf("%c is an alphabet\n",s[i]);
else
printf("%c is NOT an alphabet\n",s[i]);
i++;
}
return 0;
}
Output
1 is NOT an alphabet
2 is NOT an alphabet
3 is NOT an alphabet
a is an alphabet
b is an alphabet
c is an alphabet
! is NOT an alphabet
@ is NOT an alphabet
# is NOT an alphabet
iscntrl
int iscntrl(int c)
iscntrl(x) will be true when x is a control character.
A control charater is a character that doesn’t occupy a printing space. It means that it is a non-printing charater. Some of the control characters are ‘\0’, ‘\t’, ‘e’, etc.
#include <stdio.h>
#include <ctype.h>
int main()
{
char s[] = "Hello\nBlogsDope\n";
int i = 0;
while(s[i] != '\0')
{
if(iscntrl(s[i]))
printf("%c is a control character\n",s[i]);
else
printf("%c is NOT a control character\n",s[i]);
i++;
}
return 0;
}
H is NOT a control character
e is NOT a control character
l is NOT a control character
l is NOT a control character
o is NOT a control character
is a control character
B is NOT a control character
l is NOT a control character
o is NOT a control character
g is NOT a control character
s is NOT a control character
D is NOT a control character
o is NOT a control character
p is NOT a control character
e is NOT a control character
is a control character
isdigit
int isdigit(int c)
isdigit(x) will be true when x is a decimal digit.
#include <stdio.h>
#include <ctype.h>
int main()
{
char s[] = "123abc!@#";
int i = 0;
while(s[i] != '\0')
{
if(isdigit(s[i]))
printf("%c is a digit\n",s[i]);
else
printf("%c is NOT a digit\n",s[i]);
i++;
}
return 0;
}
1 is a digit
2 is a digit
3 is a digit
a is NOT a digit
b is NOT a digit
c is NOT a digit
! is NOT a digit
@ is NOT a digit
# is NOT a digit
isgraph
int isgraph(int c)
isgraph(x) will be true when x has a graphical representation.
All printable characters have graphical representation except the space character (‘ ’).
#include <stdio.h>
#include <ctype.h>
int main()
{
char s[] = "123abc!@ \n #";
int i = 0;
while(s[i] != '\0')
{
if(isgraph(s[i]))
printf("%c has graphical representation\n",s[i]);
i++;
}
return 0;
}
1 has graphical representation
2 has graphical representation
3 has graphical representation
a has graphical representation
b has graphical representation
c has graphical representation
! has graphical representation
@ has graphical representation
# has graphical representation
islower
int islower(int c)
islower(x) will be true when x is in the lowercase.
#include <stdio.h>
#include <ctype.h>
int main()
{
char s[] = "BlogsDope";
int i = 0;
while(s[i] != '\0')
{
if(islower(s[i]))
printf("%c is in lowercase\n",s[i]);
else
printf("%c is NOT in lowercase \n",s[i]);
i++;
}
return 0;
}
B is NOT in lowercase
l is in lowercase
o is in lowercase
g is in lowercase
s is in lowercase
D is NOT in lowercase
o is in lowercase
p is in lowercase
e is in lowercase
isprint
int isprint(int c)
isprint(x) will be true when x is a printable character (opposite of ‘iscntrl’).
#include <stdio.h>
#include <ctype.h>
int main()
{
char s[] = "Blogs\nDope";
int i = 0;
while(s[i] != '\0')
{
if(isprint(s[i]))
printf("%c is printable\n",s[i]);
else
printf("%c is NOT printable\n",s[i]);
i++;
}
return 0;
}
B is printable
l is printable
o is printable
g is printable
s is printable
is NOT printable
D is printable
o is printable
p is printable
e is printable
ispunct
int ispunct(int c)
punct(x) will be true when x is a punctuation character.
#include <stdio.h>
#include <ctype.h>
int main()
{
char s[] = "Hello, BlogsDope!";
int i = 0;
while(s[i] != '\0')
{
if(ispunct(s[i]))
printf("%c is a punctuation character\n",s[i]);
else
printf("%c is NOT a punctuation character\n",s[i]);
i++;
}
return 0;
}
H is NOT a punctuation character
e is NOT a punctuation character
l is NOT a punctuation character
l is NOT a punctuation character
o is NOT a punctuation character
, is a punctuation character
is NOT a punctuation character
B is NOT a punctuation character
l is NOT a punctuation character
o is NOT a punctuation character
g is NOT a punctuation character
s is NOT a punctuation character
D is NOT a punctuation character
o is NOT a punctuation character
p is NOT a punctuation character
e is NOT a punctuation character
! is a punctuation character
isspace
int isspace(int c)
isspace(x) will be true when x is a white-space character e.g.- ‘ ’, ‘\t’, ‘\n’, ‘\v’, etc.
#include <stdio.h>
#include <ctype.h>
int main()
{
char s[] = "Hello, BlogsDope!\n";
int i = 0;
while(s[i] != '\0')
{
if(isspace(s[i]))
printf("%c is a white-space\n",s[i]);
else
printf("%c is NOT a white-space\n",s[i]);
i++;
}
return 0;
}
H is NOT a white-space
e is NOT a white-space
l is NOT a white-space
l is NOT a white-space
o is NOT a white-space
, is NOT a white-space
is a white-space
B is NOT a white-space
l is NOT a white-space
o is NOT a white-space
g is NOT a white-space
s is NOT a white-space
D is NOT a white-space
o is NOT a white-space
p is NOT a white-space
e is NOT a white-space
! is NOT a white-space
is a white-space
isupper
int isupper(int c)
isupper(x) will be true if x is in the uppercase.
#include <stdio.h>
#include <ctype.h>
int main()
{
char s[] = "BlogsDope";
int i = 0;
while(s[i] != '\0')
{
if(isupper(s[i]))
printf("%c is in uppercase\n",s[i]);
else
printf("%c is NOT in uppercase\n",s[i]);
i++;
}
return 0;
}
B is in uppercase
l is NOT in uppercase
o is NOT in uppercase
g is NOT in uppercase
s is NOT in uppercase
D is in uppercase
o is NOT in uppercase
p is NOT in uppercase
e is NOT in uppercase
isxdigit
int isxdigit(int c)
isxdigit(x) will be true when x is a hexadecimal digit.
Any digits of 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, a, b, c, d, e, f, A, B, C, D, E and F are hexadeciaml digits.
#include <stdio.h>
#include <ctype.h>
int main()
{
char s[] = "asd123!@#";
int i = 0;
while(s[i] != '\0')
{
if(isxdigit(s[i]))
printf("%c is a hexadecimal\n",s[i]);
else
printf("%c is NOT a hexadecimal\n",s[i]);
i++;
}
return 0;
}
a is a hexadecimal
s is NOT a hexadecimal
d is a hexadecimal
1 is a hexadecimal
2 is a hexadecimal
3 is a hexadecimal
! is NOT a hexadecimal
@ is NOT a hexadecimal
# is NOT a hexadecimal
tolower
int tolower(int c)
tolower(x) converts x into lowercase.
#include <stdio.h>
#include <ctype.h>
int main()
{
printf("%c\n",tolower('A'));
return 0;
}
a
toupper
int toupper(int c)
toupper(x) converts x into uppercase.
#include <stdio.h>
#include <ctype.h>
int main()
{
printf("%c\n",toupper('a'));
return 0;
}
A
