Thread: Lesson: Binary conversion n back again

Can you use bitwise operators?

It's still easy if you do it on paper:

example: 101011010
integer value = 0*2^0 + 1*2^1 + 0*2^2 + 1*2^3... + 1*2^8

It's the same concept as the one in base 10:
3129
= 9*10^0 + 2*10^1 + 1*10^2 + 3*10^3
= 9 * 1 + 2 * 10 + 1 * 100 + 3 * 1000

I dispair if your teacher did teach you to do it that way....

1110101 = 117....not 85..

Code:

#include <iostream>
#include <cstring>
using std::cout;
using std::endl;

void ToBin(int x){
	const int mask = 1 << ((8 * sizeof(int))-1);	

	while(x){
		cout << ((mask & x)?'1':'0');
		x <<= 1;
	}
	cout << endl;
}

void ToDec(char* y){

	int mult = 1,
		total = 0;
	int len = strlen(y);
	char* c = y + len - 1;

	for(int i = 0;i<len;i++,c--){
		if((char)*c == '1')
			total += 1*mult;
		mult *= 2;
	}

	cout << total << endl;
}

int main( void )
{
	ToBin(85);

	ToDec("1010101");

return 0;
}

Here's one quick way of converting to and fro....

>> 1110101 = 117....not 85..

That's because 2 \ 2 = 1 1

should be 2 / 2 = 1 0

According to her

78 in binary is:

1001110

Yes that's right.

>>do i REALLY need this in my career?
Yes

>>I had a chart showing the binary of each number up to 10 but i lost it.
F*** the chart.

Originally posted by Ride -or- Die
Ok lemme give u one of her off-the-board ones cause i may have done that wrong.

According to her

78 in binary is:

1001110

I had a chart showing the binary of each number up to 10 but i lost it.

Yeah I get to teach someone something.

CONVERSIONS ARE EASY.

can you muliply by 2? Then you can convert decimal to binary.

start with 1 then start multiplying by 2.

1 2 4 8 16 32 64 128 256 512 1024 2048 ...... you can go on forever.

Now reverse these numbers.
64 32 16 8 4 2 1 and line up your binary number to the right.
1 0 0 1 1 1 0
64 + 8 + 4 + 2 = 78 wasnt that easy?

going the other way is easy too, not as easy. Start with the bigest number that is smaller than the number you want to find. So 64. Thats a 1. Now subtract 64 from 78 = 14 now find the largest number that is less that 14. 8. 14-8 = 6. so 4 then 2. You get the idea.

I find this to be the most easy to understand method.

When i say 64 is a one, we are just building our binary number. We mark (on our number chart) a 1 for the number we use and 0 for the numbers we dont use.

So lets take another numer say 115.

On our scale 128 > 115 so its too big. (its a 0)
115 > 64 so 64 will be marked as a 1. (we use it to make our binary number. )

Then we subtract 64 from 115 = 51. So using the same logic. we mark a 1 under the 32. Because 32 is the biggest number that is smaller than 51. Then we subtract the 32 that we used. And we have 19 left to deal with.

So our next number will be 16 (smaller than 19). We mark it with a 1. and subtract 16. to get 3.

What is the biggest number on our chart smaller than 3? 2 so we mark a 1 under 2. Now 8 and 4 were skipped, so mark them with a 0.

we subtract 2 and that leaves 1 so mark the 1 with a 1.


64 32 16 8 4 2 1

1 1 1 0 0 1 1



so we see that 64 + 32 + 16 + 2 + 1 = 115.


Does that make sense?

Originally posted by Ride -or- Die

but to take say 101011010(random) and make it a regular number, i'm lost, any help? [/B]

Let's do this one. First draw our number chart.

1024 512 256 128 64 32 16 8 4 2 1


Then starting from the right draw your binary numbers underneath it putting a 1 or a 0 under each number starting at the 1.

1024--512--256--128--64--32--16--8--4--2--1
-------------1----0----1---0---1---1--0--1--0

then just add up all the numbers that have a 1 under them.

256 + 64 +16 + 8 + 2 = 346