C isalnum function checks its argument is either a letter of the alphabet or a digit

Syntax

C isalnum function has the following syntax.

int isalnum(int ch);

C isalnum function is from the header file ctype.h.

Description

C isalnum function returns nonzero if its argument is either a letter of the alphabet or a digit.

Example

The following code uses the C isalnum function to check if a character is a letter or number. The letter itself is got from the user input. If the input is . the program will exit.


#include <ctype.h>
#include <stdio.h>
/*from  www . j  a v  a2  s  .  c o  m*/
int main(void)
{
  char ch;

  printf(". to exit:");
  for(;;) {
    ch = getc(stdin);
    if(ch == '.')
       break;
    if(isalnum(ch))
       printf("%c is alphanumeric\n", ch);
  }
  return 0;
}

The code above generates the following result.





















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assert.h
ctype.h
math.h
setjmp.h
signal.h
stdio.h
stdlib.h
string.h
time.h
wctype.h