Thread: odd function is odd

I am trying to learn how to call and write functions using an old book, "C By Discovery" It is a good book.

My problem is the following code returns the 'odd' message only on the numbers 3, and 11. At times the prog will return others but they aren`t consistent and I haven`t gotten 9, 17, and 19 to show up as odd at all.

Code:

#include <stdio.h>
#include <stdlib.h>

int main()
{
    int  inputint;

    printf ("Enter a positive even ");
    printf ("number that is less than 20.\n");

    scanf  ("%d", &inputint);

    if (inputint < 20) {
        if ( odd(inputint) )
            printf ("Sorry that number wasn`t even.\n");
        else if (inputint <= 0)
            printf ("That number wasn`t positive.\n");
    }
    else
            printf ("That number was too big.\n");

    system("PAUSE");
    return 0;

}

/* ******************odd***************************** */
/*  odd() returns a 1 if intvar is odd
*/

    odd (int intvar)
    {
            return(intvar & 2);
    }

I`m using CodeBlocks with Mingw compiler. I also tried this on DevC++ and it does the same thing. The compiler griped right at first that I was using an 'implicit' function but then carried on to run the program with the above mysteries.

Is this because this 'odd' function is an implicit function? If so how do I make it an explict function?

Thanks, Plain

Your main problem is not caused because odd() is implicitly declared, although you should always explicitly declare your functions, and their return types. If your book encourages functions as you posted above, you really should get a newer one. For explicitly declaring, do something like:

Code:

int odd(int);
int main(void)
{
...
}
int odd(int intvar)
{
...
}

You can also just put the function itself above main(); but make sure you explicitly tell the compiler that it returns int. Leaving the int off is acceptable in the older C standard, but I can think of no logical reason to do so. Be explicit so your code is more clear.

Anyway, the problem is in your odd() function. Do you know what that code does? It appears that you're mixing two different ways to determine whether a number is odd. The first way is to divide by two and check the remainder (the % operator does this). The second is to check the value of the least significant bit (bitwise anding with 1 does this; & is the bitwise and operator). So either change your & to a %, or your 2 to a 1. But make sure you understand what's going on when you do that.

Kermit and cas!
Thank You!

I can`t believe I had the wrong operator in the function! The program works now perfectly with % instead of &. What a dope! I appreciate you guys help! And yes the book is old and doesn`t use int before integer variables. I didn`t know I could add it to 'odd' but now I do.



Plain