Question

How do I write a C program called binary that takes a single command line argument, and integer, in decimal, and prints out the binary representation of the number with 64 bits. The argument must be stored as a long. Use atol to convert the command line argument.

Include a function

char *binary(long n, char *b) {

...

}

that stores the binary representation in the string b with '0's and '1's. It is the responsibility of the calling program (which will be main) to allocate a string of large enough size (65) to hold the string. The function will return b. This allows it to be called like this: printf("%s\n", binary(n, b));

You must use bit operations, in particular, anding with a mask, to examine the ith bit.

Sample runs:

calvin 09:48:30 > ./binary

usage: binary n

calvin 09:48:35 > ./binary 100

0000000000000000000000000000000000000000000000000000000001100100

calvin 09:48:42 > ./binary 0

0000000000000000000000000000000000000000000000000000000000000000

Answer 1

Here's the code:

#include<bits/stdc++.h>
using namespace std;

char *binary(long n, char *b) {
int curr_idx = 63;
while(n){
if(n%2 == 0){
b[curr_idx] = '0';
}
else{
b[curr_idx] = '1';
}
n = n/2;
curr_idx--;
}
return b;
}

int main(int argc, char * argv[]){
long n = atol(argv[1]);
char b[65];
// fill with 0's initially
for(int i = 0; i < 65; i++){
b[i] = '0';
}
b[64] = '\0'; // last null terminator
printf("%s\n", binary(n, b));
}

Answer 2

Hello, I have done the question and it is working perfectly fine. I have tried to name the variables in a proper manner to give you a better understanding for the code. I am also attaching the sample input/output file as well. It took me a lot of time to answer this. Please give me an upvote.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

char* long_to_binary(unsigned long k)

{
static char c[65];
c[0] = '\0';

unsigned long val;
for (val = 1UL << (sizeof(long)*8-1); val > 0; val >>= 1)
{   
strcat(c, ((k & val) == val) ? "1" : "0");
}
return c;
}

int main(int argc, char *argv[]){
if(argc<=1){
printf("usage: binary n");
return 0;
}
long number = atol(argv[1]);
  
//We cannot use a signed long to calculate the binary values so we have to typecast the value.
printf("%s\n",long_to_binary((unsigned long)number));
}

Sample input/output file:-