In my books, I use the binbin() function to display binary values. It’s a good way to demonstrate some of the C language’s low-level bitwise functions: The binbin() function lets you see the effect of bitwise operations at a binary level, all those ones and zeros.

Over the years, I’ve messed with the binbin() function. Here’s the current version, which I now call binString():

char *binString(unsigned short n)
{
    static char bin[17];
    int x;

    for(x=0;x<16;x++)
    {
        bin[x] = n & 0x8000 ? '1' : '0';
        n <<= 1;
    }
    bin[16] = '\0';

    return(bin);
}

The binString() function accepts an unsigned short integer as input, variable n inside the function. The short variable has a bit width of 16, so the string created is 16-characters long. The bin[] char array holds output string, plus one extra position for the null character, \0, at the end of the string. It’s a static char array, so its value is retained after the function call.

Within the function, a for loop processes each bit in value n. The binary & (AND) operator compares the far left bit with 1 and sets the character ‘1’ or ‘0’ depending on the bit’s value. Value n is then shifted left one bit position and the loop continues. The result is a string representing the bit values stored in n, which is returned from the function.

Here is the full code I use to test the binString() function:

#include <stdio.h>

char *binString(unsigned short n)
{
    static char bin[17];
    int x;

    for(x=0;x<16;x++)
    {
        bin[x] = n & 0x8000 ? '1' : '0';
        n <<= 1;
    }
    bin[16] = '\0';

    return(bin);
}

int main()
{
    unsigned short value;

    printf("Enter an integer value, 0 to 65535: ");
    scanf("%hd",&value);

    printf("Decimal value is %d\n",value);
    printf("Octal value is %o\n",value);
    printf("Hexadecimal value is 0x%X\n",value);
    printf("Binary value is %s\n",binString(value));

    return(0);
}

Sample run:

Enter an integer value, 0 to 65535: 43690
Decimal value is 43690
Octal value is 125252
Hexadecimal value is 0xAAAA
Binary value is 1010101010101010

I use the binbin() version of the binString() function in my book, Beginning Programming with C For Dummies, to demonstrate the various bitwise functions in C. The binString() function improves upon it by returning a full string, but the result is the same: a string representation of bits. This complements the natural capability of the C language to output decimal, octal, and hexadecimal.

But what about the other way?

For example, you can input decimal, octal, and hexadecimal values into a C program, but you can’t input binary.

The following code accepts hexadecimal input:

#include <stdio.h>

int main()
{
    unsigned n;

    printf("Type a hex value: ");
    scanf("%x",&n);
    printf("You typed %X, which is %d\n",n,n);

    return(0);
}

The %x directs the scanf() function to read hexadecimal values. Here’s the sample run:

Type a hex value: AA
You typed AA, which is 170

You could change the %x in the scanf() function to %o to input octal values or %d to input decimal values. What you cannot do, however, is use a % placeholder to read in a binary value. That’s a topic I tackle in next week’s Lesson.