Decimal To Binary in C Char Array - c

Question

I want to return a 16BIT binary from a decimal number. I havt 2 Codes.
In the first one I tried to return a char array.
In the second one a have an output but it in the inverse order.
Maybe someone take a look at the codes.
Thanks
Output first Function: Þ0000000000010000es (x862uÿ¼×
#include <stdio.h>
#include <stdlib.h>
const int BIT = 16;
void binary(int);
char *bin(int);
int main() {
binary(16);
printf("\n");
printf("%s\n", bin(16));
return 0;
}
char *bin(int x) {
char * new = (char*)malloc(sizeof(char) * BIT + 1);
new[BIT] = '\0';
if (x >= 0 && x <= 65535) {
for (int i = 0; i < BIT; i++) {
if (x % 2 == 0) {
new[BIT - i] = '0';
} else {
new[BIT - i] = '1';
}
x = x / 2;
}
}
return new;
}
void binary(int x) {
if (x >= 0 && x <= 65535) {
for (int i = 0; i < BIT; i++) {
if (x % 2 == 0) {
printf("0");
} else {
printf("1");
}
x = x / 2;
}
}
}

Answer 1

I try to answer your question. I am not interested in anybody down-voting me... So I do my very best!!
If you want a binary representation of a decimal value, the easiest thing is to check for bit 0 and then shift the number as long as it is non-zero. Shifting one bit to the right is the same as dividing it by 2.
Instead of checking if the number is between 0 and 65535, it is enough to look if it is zero if you want to abort. If you want a fixed amount of shifts, you can also count from 1 to 16.
So I would suggest something like this:
do {
if (number & 1) {
printf("1");
} else {
printf("0");
}
number >>= 1;
} while(number);
This would output zeros and ones in inversed direction until there are no more ones.
If you want a fixed width representation:
#define BITS 16
for (int bits = 0; bits < BITS; bits++) {
if (number & 1) {
printf("1");
} else {
printf("0");
}
number >>= 1;
}
And if you want to store it into an array, replace printf by
char *bitmap = (char*)malloc(BITS+1);
bitmap[BITS] = '\0'; // NULL termination
bitmap[BITS-1-bits] = '1';
or
bitmap[BITS-1-bits] = '0';
respectively
and have
printf("%s\n", bitmap);
Don't forget to free(bitmap).
Always consider, that an array is zero-based indexed. So it is better to
have bit numbering go from 0 to 15 in case of 16 bits.
I have not tested this code but it works like this. :)

Answer 2

this works, function bin() overwrites array arr in main() ( How do I return a char array from a function? ):
#include <stdio.h>
#include <stdlib.h>
const int BIT = 16;
void binary(int);
void bin(char*, int);
int main(int argc, char* argv[]) {
int x ;
x = atoi(argv[1]);
char arr[BIT+1];
//binary(16);
bin(arr, x); // functions overwrites array arr
arr[BIT] = '\0'; // strings have to be null-terminated in C
printf("%s \n", arr);
return 0;
}
void bin(char *arr1,int x) {
if (x >= 0 && x <= 65535)
{
for (int i = BIT-1; i >= 0; i--)
{
if (x % 2 == 0)
{
arr1[i] = '0';
} else
{
arr1[i] = '1';
}
x = x / 2;
}
}
}