Decimal to Binary conversion - c

Question

I need to convert a 20digits decimal to binary using C programming. What buffer will I create, because it will be very large, even the calculator can't compute converting 20 digits to Binary.
here is sample of what i intend to accomplish:
Let is assume this code:
I am type this value via my keyboard into the buffer. Meanwhile, I am using an AT85C55WD Mcu.
unsigned char idata token[20]=(2,3,5,6,3,3,4,4,3,2,4,4,6,7,4,3,4,5,3,3);
I want a result
type-define variable convrt_token= 23562244324467434533;
Is this possible using C? If it is, then please how do i go about it?

Answer 1

each digit in decimal has 10 values, 0..9. so you'll need between 3 and 4 digits in binary. so let's say 4 to keep it simple.
so for a 20 digit decimal you'll need an 80 digit number in binary.
you can do it all with chars to keep it simple as well. i assume this is for fun.
char decnum[20];
char binnum[80];
good luck.

Answer 2

Here is elegent solution....:)
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<math.h>
#include<unistd.h>
#include<assert.h>
#include<stdbool.h>
#define max 10000
#define RLC(num,pos) ((num << pos)|(num >> (32 - pos)))
#define RRC(num,pos) ((num >> pos)|(num << (32 - pos)))
void tobinstr(int value, int bitsCount, char* output)
{
int i;
output[bitsCount] = '\0';
for (i = bitsCount - 1; i >= 0; --i, value >>= 1)
{
output[i] = (value & 1) + '0';
}
}
int main()
{
char s[50];
tobinstr(65536,32, s);
printf("%s\n", s);
return 0;
}

Answer 3

Start off as Gidon mentions. Then you only need to define a function 'decToBin' or something like that, which you can use like this:
char decnum[20];
char binnum[80];
// ... get the values, do zero initialization etc...
decToBin( decnum, binnum );
And you're ready to go.
The decToBin function could easily be implemented as a common long division algorithm. That shouldn't be too hard.
Have fun ;)
EDIT: Detailed description:
Look at your last digit. Is it divisible by 2?
--> yes: your binary digit will be 0
--> no: your binary digit will be 1
Divide the entire decimal number by 2 (Long division preferrably) and truncate if necessary.
start over. You will get the binary digits in reverse order. (Repeat until your decimal number is 0)