Solution for Exercise 17-2

ex1702

#include <stdio.h>

char *binbin(unsigned n);

int main()
{
    unsigned input;

    printf("Type a value 0 to 65535: ");
    scanf("%u",&input);
    printf("%u is binary %s\n",
            input,binbin(input));
    return(0);
}

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

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

Output

Type a value 0 to 65535: 65000
65000 is binary 1111110111101000

Notes

* Some things I forgot to tell you in the book:

Also change the prototype for binbin() at Line 3.

Remove the typecast at Line 12 (the printf() statement starting at Line 11). This step is necessary, otherwise an unsigned char is passed to the function instead of an unsigned int value.

* Yes, the compiler doesn't complain when you pass the binbin() function an unsigned char instead of an unsigned int, but the typecast truncates the value, so only the left 8 bits are significant.

Exercise ex1703 →