C/ctype.h/isalnum

int isalnum(int ch)

<source lang="cpp">

//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.  
 
          
 #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;
 }
        

/* 2 is alphanumeric 1 is alphanumeric 1 1 is alphanumeric 2 2 is alphanumeric 12 1 is alphanumeric 2 is alphanumeric 1 1 is alphanumeric 1 1 is alphanumeric 1 1 is alphanumeric ! ~ .

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      </source>