C - Check if a letter is consonant or vowel


You could simplify the switch by making use of the isalpha() function.

The function returns a nonzero integer if the character that's passed as the argument is an alphabetic character, and it will return 0 (false) if the character isn't alphabetic.

You could therefore produce the same result as the previous switch with the following code:


#include <stdio.h>
#include <ctype.h>
int main()/* ww w .  j av  a2  s.  c  o m*/

  char ch = 'a';
  if (!isalpha(ch))
    printf("The character is not a letter.\n");
    switch (tolower(ch))
    case 'a': case 'e': case 'i': case 'o': case 'u':
      printf("The character is a vowel.\n");
      printf("The character is a consonant.\n");
  return 0;


The if statement tests for ch not being a letter, and if this is so, it outputs a message.

If ch is a letter, the switch statement will sort out whether it is a vowel or a consonant.

The five vowel case values produce one output, and the default case produces the other.

ctype.h header also declares several other useful functions for testing a character.

FunctionTests For
islower() Lowercase letter
isupper() Uppercase letter
isalnum() Uppercase or lowercase letter or a decimal digit
iscntrl() Control character
isprint() Any printing character including space
isgraph() Any printing character except space
isdigit() Decimal digit ( '0' to '9')
isxdigit() Hexadecimal digit ( '0' to '9', 'A' to 'F', 'a' to 'f')
isblank() Standard blank characters (space, '\t')
isspace() Whitespace character (space, '\n', '\t', '\v', '\r', '\f')
ispunct() Printing character for which isspace() and isalnum() return false
isalpha() Uppercase or lowercase letter
tolower() Convert to lowercase
toupper() Convert to uppercase

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