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C ctype isalnum() Function

❮ C ctype Library


Example

Check if a character is alphanumeric (a letter or number):

char c = 'A';
if (isalnum(c)) {
  printf("%c is alphanumeric", c);
} else {
  printf("%c is not alphanumeric", c);
}
Try it Yourself »

Definition and Usage

The isalnum() function returns a non-zero value (equivalent to boolean true) if a character is alphanumeric, meaning an alphabet letter (a-z) or a number (0-9).

Example of characters that are not alphanumeric: (space)!#%&? etc.

The isalnum() function is defined in the <ctype.h> header file.


Syntax

int isalnum(int c);

Parameter Values

Parameter Description
c Required. The ASCII value of a character or an actual character

Technical Details

Returns: An int value which is non-zero (equivalent to boolean true) if the character is alphanumeric.

Otherwise it returns 0 (equivalent to boolean false).

More Examples

Example

Check different characters:

void checkNum(char c) {
  if (isalnum(c)) {
    printf("%c is alphanumeric\n", c);
  } else {
    printf("%c is not alphanumeric\n", c);
  }
}

int main() {
  char char1 = 'B';
  char char2 = 'X';
  char char3 = '+';

  checkNum(char1);
  checkNum(char2);
  checkNum(char3);

  return 0;
}
Try it Yourself »

❮ C ctype Library

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