C ctype.h Library

C `ctype.h` Library

In C ctype.h Library provides functions to test and manipulate characters. It’s very useful for validating input, parsing text, and formatting strings.

All functions in ctype.h work with int values representing characters (usually char).

📌 Common Functions in `ctype.h`

1️⃣ Character Testing Functions

Function	Description	Example
`isalnum(int c)`	Checks if character is alphanumeric (a-z, A-Z, 0-9)	`isalnum('A')` → true
`isalpha(int c)`	Checks if character is alphabetic	`isalpha('1')` → false
`isdigit(int c)`	Checks if character is a digit	`isdigit('5')` → true
`islower(int c)`	Checks if character is lowercase	`islower('a')` → true
`isupper(int c)`	Checks if character is uppercase	`isupper('B')` → true
`isspace(int c)`	Checks for whitespace (`' '`, `'\t'`, `'\n'`)	`isspace(' ')` → true
`ispunct(int c)`	Checks if character is punctuation	`ispunct('!')` → true
`isxdigit(int c)`	Checks if character is hexadecimal digit	`isxdigit('F')` → true
`isprint(int c)`	Checks if character is printable	`isprint('\n')` → false
`isgraph(int c)`	Checks if character has graphic representation	`isgraph(' ')` → false

2️⃣ Character Conversion Functions

Function	Description	Example
`tolower(int c)`	Converts uppercase to lowercase	`tolower('A')` → `'a'`
`toupper(int c)`	Converts lowercase to uppercase	`toupper('b')` → `'B'`

3️⃣ Example: Character Validation and Conversion

#include <stdio.h>
#include <ctype.h>int main() {
char c;

printf("Enter a character: ");
scanf("%c", &c);

if(isalpha(c))
printf("%c is a letter.\n", c);
else if(isdigit(c))
printf("%c is a digit.\n", c);
else if(isspace(c))
printf("%c is a whitespace.\n", c);
else
printf("%c is a special character.\n", c);

printf("Uppercase: %c\n", toupper(c));
printf("Lowercase: %c\n", tolower(c));

return 0;
}

#include <stdio.h>

#include <ctype.h>int main() {

char c;

printf("Enter a character: ");

scanf("%c", &c);

if(isalpha(c))

printf("%c is a letter.\n", c);

else if(isdigit(c))

printf("%c is a digit.\n", c);

else if(isspace(c))

printf("%c is a whitespace.\n", c);

else

printf("%c is a special character.\n", c);

printf("Uppercase: %c\n", toupper(c));

printf("Lowercase: %c\n", tolower(c));

return 0;

}

Sample Output:

4️⃣ Example: Count Character Types in a String

#include <stdio.h>
#include <ctype.h>int main() {
char str[] = "Hello 123!";
int letters=0, digits=0, spaces=0, punct=0;

for(int i=0; str[i]; i++) {
if(isalpha(str[i])) letters++;
else if(isdigit(str[i])) digits++;
else if(isspace(str[i])) spaces++;
else if(ispunct(str[i])) punct++;
}

printf("Letters: %d\nDigits: %d\nSpaces: %d\nPunctuation: %d\n", letters,digits,spaces,punct);

return 0;
}

#include <stdio.h>

#include <ctype.h>int main() {

char str[] = "Hello 123!";

int letters=0, digits=0, spaces=0, punct=0;

for(int i=0; str[i]; i++) {

if(isalpha(str[i])) letters++;

else if(isdigit(str[i])) digits++;

else if(isspace(str[i])) spaces++;

else if(ispunct(str[i])) punct++;

}

printf("Letters: %d\nDigits: %d\nSpaces: %d\nPunctuation: %d\n", letters,digits,spaces,punct);

return 0;

}

Output:

📌 Summary Table

Function	Purpose
`isalnum`	Checks alphanumeric
`isalpha`	Checks alphabetic
`isdigit`	Checks digits
`islower`	Checks lowercase letters
`isupper`	Checks uppercase letters
`isspace`	Checks whitespace characters
`ispunct`	Checks punctuation
`isxdigit`	Checks hexadecimal digit
`isprint`	Checks printable characters
`isgraph`	Checks graphic characters
`tolower`	Converts to lowercase
`toupper`	Converts to uppercase

✅ Notes

Functions expect int values, usually casted from char.
Always include #include <ctype.h>.
Useful for input validation, parsing, and formatting strings.
Can be combined with string.h for advanced string processing.

C ctype.h Library

C ctype.h Library

📌 Common Functions in ctype.h

1️⃣ Character Testing Functions

2️⃣ Character Conversion Functions

3️⃣ Example: Character Validation and Conversion

4️⃣ Example: Count Character Types in a String

📌 Summary Table

✅ Notes

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📌 Common Functions in `ctype.h`