C Tutorial/ctype.h/isalnum

isalnum

Item Value Header file ctype.h Declaration int isalnum(int ch); Return returns nonzero if its argument is either a letter of the alphabet or a digit. returns zero if the character is not alphanumeric.

<source lang="cpp">#include <ctype.h>

 #include <stdio.h>
 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;
 }</source>