converting numbers/primes into binary

I want to compare some different number systems together with respect to primes. Wanted to know how to convert to binary. Thought this would be in-built to the computers/language, as all numbers are already stored as binary?

Anyway, found this forum with lots of different answers. Smallest answer was:

#include int main(void) {   int i, target;   printf("Enter a number: ");   scanf("%d", &target);   for(i = 32; i--;) {     if(target & (1 << i))       putc('1', stdout);     else       putc('0', stdout);   }   return 0; }

although they suggest altering part of it to

for(i=(j-1);i >= 0; i--) /* or 'for(i=j;i--; )' would also work but is a bit too cryptic for me to get my head round */ {   if(target & (1 << i))     putc('1', stdout);   else     putc('0', stdout); }

I shall try this out.

I ended up doing it my own way, mostly so that I could practice programming. I used the divide by 2 way, and if there is remainers then print 1, else print 0:

#define BINARYARRAYSIZE 1000

//converts a number into Binary and prints with greatest bit first

void convertAndPrintBinary (int number) {

    //printf("converting to binary\n");

    

    

    int binaryArray [BINARYARRAYSIZE] = {0};

    int i = 0;

    for (int result = number; result > 0; result = result/2) {

        

        if (result % 2 == 0 ) {

            binaryArray[i]=0;

            //printf("0");

        } else {

            binaryArray[i]=1;

            //printf("1");

        }

        

        i++;

    }

    

    //printf("%d\n", i );

    

    //prints out array in reverse

    for (int c = i-1; c >=0 ; c--) {

        printf("%d", binaryArray[c]);

    }

    

}

Worked really well in the end:

Type a starting number: 1

Type an end numbers: 20

1 = 1

2 = 10

3 = 11

4 = 100

5 = 101

6 = 110

7 = 111

8 = 1000

9 = 1001

10 = 1010

11 = 1011

12 = 1100

13 = 1101

14 = 1110

15 = 1111

16 = 10000

17 = 10001

18 = 10010

19 = 10011

20 = 10100

I used BINARYARRAYSIZE because I didn't want to run the first for loop twice; once to measure how big the array needed to be, and the second to fill it. When I didn't give the array a size to begin with, it kept erroring. But 1000 digits for binary is a large number!