Convert base 10 to base 2, C programming

问题

I'm still new with programming and I'd like to ask about one specific question about the Clanguage. I'm using codeblocks compiler.

Here is a piece of code:

int n, c, k;

scanf("%d",&n);

for(c = 31;c >= 0;c--)
{
    k = n >> c;

    if(k & 1)
        printf("1");
    else
        printf("0");
}

return 0;

that I got from one website and it converts the base to the binary one.

My question is, where I have an if&else statement, why is there if(k & 1) printf("1") ?? I thought that k can be both 1 and 0 and if I use (k & 1) there are two options such as (0 & 1) = 0 and (1 & 1) = 1. Can please anybody explain me this? Thank you very much.

回答1:

The expression inside of an if statement always evaluates to true or false. In terms of integers, 0 means false, and anything non-zero means true. When you have k & 1, that means that if the least-significant bit of k is 1, then that expression evaluates to 1 and is therefore considered true. If the least-significant bit of k is 0, then the expression evaluates to 0 and is therefore considered to be false.

回答2:

One thing that helped me when I was starting was to 'manually' run through the code a few times with pen-and-paper.

To give you an example, lets consider your loop (but work with 8-bit integers rather than 32-bit integers):

for(c = 7; c >= 0; c--)
{
    k = n >> c;
    if(k & 1)
        printf("1");
    else
        printf("0");
}

I am assuming the other code in your example doesn't change. Furthermore, assume that the user entered 218 (or 11011010 in binary).

first iteration:

n is 218, c is 7.
we do a right shift 7 (n >> c) which makes k 00000001
we do a bit-wise `and' of k and 1 (K & 1), which is 1 or true
we print "1"

second iteration:

n is 218, c is 6.
we do a right shift 6 (n >> c) which makes k 00000011
we do a bit-wise `and' of k and 1 (k & 1), which is 1 or true
we print "1"

third iteration:

n is 218, c is 5.
we do a right shift 5 (n >> c) which makes k = 00000110
we do a bit-wise `and' of k and 1 (k&1), which is 0 or false
we print "0"

and so on...

So, you are correct that k can be either 0 or 1, however it assumes only one of those values each time through the loop.

Finally, in case you are unclear on how the bit-wise `and' works, it looks at the n-th bit in both numbers and if they are the same it sets the n-th bit of the result to one (1) otherwise it sets the result to zero (0). Consider the bit-wise and of 218 with 15:

218  is 11011010     e.g. third bit from right is zero
 15  is 00001111     e.g. third bit from right is one
-----------------
  &     00001010     e.g. third bit from right is zero

来源：https://stackoverflow.com/questions/24586632/convert-base-10-to-base-2-c-programming

标签

binary

codeblocks