Thread: Alphanumeric check

Look in ctype.h

Well, you're trying to compare one fix value with an array.
what you need is a function that tests if the specified char is alphanumeric
2 immediate ways:
you could test if the char is part of your collection with

Code:

char *strstr(const char *haystack, const char *needle);

but your collection aka array is wrong initialized, if I'm not confused, you have to initialize it like

Code:

{'1', '2', '3', '4', '5', '6', '7', '8', '9', '0'}

you also could write your own method which checks every array element if it is the same as the specified one in a for loop


Other approach: Since chars are ASCII and numbers are neighbours in ASCII Code, you can compare it like this

Code:

char c = '2'
if ('0' < c) {
   printf("%c \n", c);
}

which ought to print out 2

EDIT:

When I take a second look at your code, i see that your for-loop probably won't work this way, what are you trying to accomplish? What is safed in test_pass?
if test_pass is an array, as i suppose, then you have to init the for head in another way. You want to start with first letter, which will be a position 0, so you init i at zero
Till when you want to check this string? To the end? than you have to continue loop until your 'i' which represents one char of your string, is the same position as the length of your string / array
for example:

Code:

char str[] = "Hello World";
for (int i = 0;i < strlen (str) ; i++) /* ++i or i++ doesn't really matter */
{
    printf("%c", str[i]);
}

The compiler isn't happy, because the loop is treating test_pass like an int, but the body of the loop is treating it like an array or a pointer. That is impossible - there is no type in C with that combination of properties.

Assuming test_pass is an array (not an int) the if() statement may actually compile. However, it won't do anything like what you expect. The comma operator - used in an expression like "a,b" evaluates a, discards it, and then gives the result of b. The brackets simply stop interactions with other operators of different precedence, and yields the result of whatever is enclosed. So "if(test_pass[i] == ('1', '2', '3', '4', '5', '6', '7', '8', '9', '0'))" is equivalent to "if(test_pass[i] == '0')

Look up isnum() and isalpha() functions in the standard header <ctype.h>. They provide a means of testing single characters are numeric or alphabetic, respectively. They don't work on arrays though - you will need to work out how to apply those functions to every element in an array.





Seriously, though, you need to read a basic textbook on C before you provide more code. Your code here is obviously produced by pure guesswork. That is not a good way to learn (since you won't understand why the compiler complains or code doesn't work). It is also a way to seriously discourage people from helping you in forums, since it demonstrates low effort by you to learn, while expecting people to expend considerably more effort than you do, in order to help you.

I didn't advise you to do that.

Buying a textbook was a good idea .... assuming you acquired a reasonable one. There are some pretty terrible ones around.

Incidentally, "containing digits" and "alphanumeric" are not equivalent concepts.

You can also use the function 'isdigit()':

Code:

#include <ctype.h>
…
if ( isdigit(char[i]) )
{
    /* do whatever */
}

Originally Posted by MutantJohn

I'm using this table : ASCII and Binary Characters (The Characters)

And it seems like all character numbers have a value from 48 to 57.

Couldn't you just iterate the string and do simple checks? Like,

Code:

if (char[i] >= 48 && char[i] <= 57)
{
    /* do whatever */
}

Not all implementations employ ASCII, or related, character sets.

Originally Posted by MutantJohn

And it seems like all character numbers have a value from 48 to 57.

Couldn't you just iterate the string and do simple checks?

In the special case of the digits, you can indeed compare for the value being between '0' and '9', since that is guaranteed. However, comparing for the value being 48 and 57 is a bad idea, both because of the use of magic numbers and because those values depend on character set. Furthermore, other than for the digits, comparison for say, 'a' to 'z' makes assumptions that might not hold true.