The function toupper() returns a uppercase character of the character that is put in.

toupper() source code example:

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The function tolower() returns a lowercase character of the character that is put in.

tolower() source code example:

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The function isxdigit() returns a non-zero if its argument is a hexadecimal digit. (If the argument is a: a-f, A-F, or 0-9).
If the argument is not a hexadecimal digit, then zero is returned.

isxdigit() source code example:

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The isupper() function returns a non-zero if its argument is an uppercase letter.
If the argument is not an uppercase letter, then zero is returned.

isupper() source code example:

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The isspace() function returns a non-zero if its argument is a single space, newline, tab, form feed, vertical tab, or carriage return.

If the argument is not a single space, newline, tab, form feed, vertical tab, or carriage return , then zero is returned.

isspace() source code example:

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The ispunct() function returns a non-zero if its argument is a punctuation character. (All characters except alphanumeric or white-space). If the argument is not a punctuation character, then zero is returned.

ispunct() source code example:

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The function isprint() returns a non-zero if its argument is a printable character (including a white-space). If the argument is not a printable character (like the newline character ‘\n’ ) , then zero is returned.

isprint() source code example:

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The islower() function returns a non-zero if its argument is a lowercase letter. If the argument is not a lowercase letter, then zero is returned.

islower() source code example:

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The function isgraph() checks if parameter is a character with graphical representation that can be printed. Whitespace characters like space are skipped. If the argument is not, then zero is returned.

isgraph() source code example:

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The function isdigit() returns a non-zero if its argument is a digit between 0 and 9. If its argument is not a digit between 0 and 9, then zero is returned.

isdigit() source code example:

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