C decimal to binary without arrays - c++

Question

I think I've almost got it, but I feel like I'm go in circles trying to figure this out.
The challenge to out cout without using strings or arrays. I took the number 56 as an example and 56 should equal 111000 this is not the case as it goes through fine till 7 then the number equals number*2 + number%2 makes it equal to 15 and outputs all 1's. Idk anymore, this is driving me to the moon and back.
#include <iostream>
using namespace std;
int main()
{
int number = 0;
int n = 1;
int x = n;
cin>>number;
cout<<n%2;
while(n <= number)
{
if(n%2 == 0)
{
n = n*2;
cout<<0;
}
else
{
n = n*2 + n%2;
cout<<n%2;
}
}
}

Answer 1

You can use the binary operator & to check if a single bit is 1 or 0.
for (int i=512; i>0; i/=2) {
cout << ( ( number & i ) != 0 ) ;
}
Note that this WILL print leading 0's.
Also, I'm assuming you only want to print positive integers.
Alternative:
for (int i=512; i>0; i/=2) {
if (number >= i) {
cout << 1;
number -= i;
} else {
count << 0;
}
}

Answer 2

You can use recursion
void decimal_to_binary(int decimal)
{
int remainder = decimal % 2;
if (decimal < 1)
return;
decimal_to_binary(decimal / 2);
cout << remainder;
}
This function will take the decimal, get its remainder when divided to 2. Before it the function call itself again, it checks if the decimal is less than 1(probably 0) and return to execute the printing of 1's and 0's

Answer 3

I had this type of problem assigned to me recently. This code example work up to a maximum of 10 binary digits (per the problem guidelines) and keep prompting for input until 0 is entered (sentinel value). This can certainly be improved but the math is correct:
#include <iostream>
#include <cmath>
using namespace std;
int main ()
{
//Declare Variables
int inputValue = 0;
int workingValue = 0;
int conversionSum = 0;
//Begin Loop
do{
//Prompt for input
cout << "Enter a binary integer (0 to quit): ";
cin >> inputValue;
//Reset Variables
workingValue = inputValue;
conversionSum = 0;
//Begin processing input
//10 digits max, so 10 iterations
for (int i=0; i<10; i++) {
//Check for non-binary entry
if ((workingValue % 10) != 1 && (workingValue % 10 != 0)){
cout << "Invalid!\n";
workingValue = 0;
conversionSum = 0;
break;
}
//check to see if 2^i should be added to sum
if (workingValue%2 == 1){
conversionSum += pow(2,i);
workingValue--;
}
//divide by 10 and continue loop
workingValue= workingValue / 10;
}
//output results
cout << "converted to decimal is: " << conversionSum << endl;
}while (inputValue != 0);
}

Answer 4

#include<iostream>
#include<cmath>
using namespace std;
int main()
{
cout << "enter a number";
int number, n, a=0;
cin >> number;
n = number;
do
{
n=n/2;
a=a+1;
}
while (n>=1);
cout << "a is" << a;
int c = a;
int b = a;
cout << "binary is";
for(int i=0; i<=c; i++)
{
int k = number / pow(2,b);
cout << k;
number = number - k * pow(2,b);
b = b-1;
}
return 0;
}
Although asked in C I have used C++. I have used the logic that if you have to convert decimal to binary we have to find the maximum power of 2 contained in the number which when added by 1 becomes the number of digit of required binary .. leftmost digit is the number of highest available power of 2 (ex in 8 highest power of 2 is 3 and 1 such is available)...then subtract this from the number and (ex 8-8=0)and search for number of next highest available power of 2 and so on.