Question

char dict[N][M];

for(i = 0; i < N; i++)
{
    do
    {
        printf("enter word at position: %d\n", i);    
        gets(dict[i]);
        printf("you entered %s\n", dict[i]);    

        if(isalnum(dict[i]))
        {
            printf("error\n");
        }
    }while (isalnum(dict[i]));    
}

Hello I’m new to C and I want to do validation with isalnum but with a 2d array
for example if dict[0][80] is non alphanumeric the user enter again.

Thanks

Answer 1

Your compiler should print a warning similar to this when you try to compile your code:

warning: passing argument 1 of ‘isalnum’ makes integer from pointer without a cast.

This warning is a sign that the code isn’t doing what you want, and here’s why. The signature of the “isalnum” function is int isalnum(int c) which means it takes an integer (i.e. character) argument; however, you’re calling it with the argument dict[i], which is a char * (a pointer to a character, e.g. a string).

I’m guessing what you want to do is check that each character in the string is alphabetic or numeric. Try replacing your call to “isalnum” with your own function like so:

/* Returns true iff each character of "s" is alphabetic or numeric. */
int str_isalnum(char * s) {
  int i=0, len=strlen(s);
  for (i=0; i<len; i++) {
    if (!isalnum(s[i])) return 0; /* false */
  }
  return 1; /* true */
}

/* ... */
  printf("you entered %s\n", dict[i]);    
  if (!str_isalnum(dict[i])) {
    printf("error\n");
  }
} while (!str_isalnum(dict[i]));