C printing bits

Question

I am trying to write a program in C that prints bits of int. for some reason i get wrong values,

void printBits(unsigned int num){
    unsigned int size = si         


        

Answer 1

How about this Macro:

#define print_bits(x) \
do { \
        unsigned long long a__ = (x); \
        size_t bits__ = sizeof(x) * 8; \
        printf(#x ": "); \
        while(bits__--) putchar(a__ & (1 << bits__) ? '1' : '0'); \
        putchar('\n'); \
} while(0)

Use like:

char c = 3;
int i = -1;
print_bits(c);
print_bits(i);

output:

c: 00000011
i: 11111111111111111111111111111111

If you don't want to print the expression 'x' which is the argument to 'print_bits' remove the line:

printf(#x ": "); \

This Marco can be used on any primitive datatype and the expression 'x' will be evaluated only once. So you should be safe from side effects.

Answer 2

You are calculating the result correctly, but you are not printing it right. Also you do not need a second loop:

for(;i<size*8;++i){
    // print last bit and shift left.
    printf("%u ",num&maxPow ? 1 : 0);
    num = num<<1;
}

If you'd like to show off, you could replace the conditional with two exclamation points:

printf("%u ", !!(num&maxPow));

Answer 3

The result you get is because num&maxPow is either 0 or maxPow. To print 1 instead of maxPow, you could use printf("%u ", num&maxPow ? 1 : 0);. An alternative way to print the bits is

while(maxPow){
    printf("%u ", num&maxPow ? 1 : 0);
    maxPow >>= 1;
}

i.e. shifting the bitmask right instead of num left. The loop ends when the set bit of the mask gets shifted out.

Answer 4

To address point two, I'd consider the following, which is simplified a bit for ease of understanding.

void printBits(unsigned int num)
{
   for(int bit=0;bit<(sizeof(unsigned int) * 8); bit++)
   {
      printf("%i ", num & 0x01);
      num = num >> 1;
   }
}

Answer 5

void print_bits(unsigned int x)
{
    int i;
    for(i=8*sizeof(x)-1; i>=0; i--) {
        (x & (1 << i)) ? putchar('1') : putchar('0');
    }
    printf("\n");
}