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C - Single Character Library Functions

In C, there are several single-character library functions available for character manipulation. These functions allow you to perform various operations on individual characters. Here are some common single-character library functions along with illustrations for each one:

1. isalpha - Checks if a character is an alphabetic character (a letter):

#include <stdio.h>
#include <ctype.h>

int main() {
    char ch = 'A';

    if (isalpha(ch)) {
        printf("%c is an alphabetic character.\n", ch);
    } else {
        printf("%c is not an alphabetic character.\n", ch);
    }

    return 0;
}

2. isdigit - Checks if a character is a digit (0-9):

#include <stdio.h>
#include <ctype.h>

int main() {
    char ch = '5';

    if (isdigit(ch)) {
        printf("%c is a digit.\n", ch);
    } else {
        printf("%c is not a digit.\n", ch);
    }

    return 0;
}

3. isalnum - Checks if a character is alphanumeric (a letter or a digit):

#include <stdio.h>
#include <ctype.h>

int main() {
    char ch = 'X';

    if (isalnum(ch)) {
        printf("%c is alphanumeric.\n", ch);
    } else {
        printf("%c is not alphanumeric.\n", ch);
    }

    return 0;
}

4. islower - Checks if a character is a lowercase letter:

#include <stdio.h>
#include <ctype.h>

int main() {
    char ch = 'z';

    if (islower(ch)) {
        printf("%c is a lowercase letter.\n", ch);
    } else {
        printf("%c is not a lowercase letter.\n", ch);
    }

    return 0;
}

5. isupper - Checks if a character is an uppercase letter:

#include <stdio.h>
#include <ctype.h>

int main() {
    char ch = 'Q';

    if (isupper(ch)) {
        printf("%c is an uppercase letter.\n", ch);
    } else {
        printf("%c is not an uppercase letter.\n", ch);
    }

    return 0;
}

6. tolower - Converts an uppercase character to lowercase:

#include <stdio.h>
#include <ctype.h>

int main() {
    char ch = 'A';

    char lowercase = tolower(ch);

    printf("%c converted to lowercase is %c.\n", ch, lowercase);

    return 0;
}

7. toupper - Converts a lowercase character to uppercase:

#include <stdio.h>
#include <ctype.h>

int main() {
    char ch = 'z';

    char uppercase = toupper(ch);

    printf("%c converted to uppercase is %c.\n", ch, uppercase);

    return 0;
}

These functions are part of the ctype.h library and are useful for character classification and conversion operations in C programs.

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