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 = sizeof(unsigned int);
    unsigned int maxPow = 1<<(size*8-1);
    printf("MAX POW : %u\n",maxPow);
    int i=0,j;
    for(;i<size;++i){
        for(j=0;j<8;++j){
            // print last bit and shift left.
            printf("%u ",num&maxPow);
            num = num<<1;
        }
    }
}

My question, first why am i getting this result (for printBits(3)).

MAX POW : 2147483648 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 2147483648 214748364 8

second is there a better way to do this ?

Answer 1

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));