C++ - Decimal to binary converting

I wrote a 'simple' (it took me 30 minutes) program that converts decimal number to binary. I am SURE that there's a lot simpler way so can you show me? Here's the code:

#include <iostream>
#include <stdlib.h>

using namespace std;
int a1, a2, remainder;
int tab = 0;
int maxtab = 0;
int table[0];
int main()
{
    system("clear");
    cout << "Enter a decimal number: ";
    cin >> a1;
    a2 = a1; //we need our number for later on so we save it in another variable

    while (a1!=0) //dividing by two until we hit 0
    {
        remainder = a1%2; //getting a remainder - decimal number(1 or 0)
        a1 = a1/2; //dividing our number by two
        maxtab++; //+1 to max elements of the table
    }

    maxtab--; //-1 to max elements of the table (when dividing finishes it adds 1 additional elemnt that we don't want and it's equal to 0)
    a1 = a2; //we must do calculations one more time so we're gatting back our original number
    table[0] = table[maxtab]; //we set the number of elements in our table to maxtab (we don't get 10's of 0's)

    while (a1!=0) //same calculations 2nd time but adding every 1 or 0 (remainder) to separate element in table
    {
        remainder = a1%2; //getting a remainder
        a1 = a1/2; //dividing by 2
        table[tab] = remainder; //adding 0 or 1 to an element
        tab++; //tab (element count) increases by 1 so next remainder is saved in another element
    }

    tab--; //same as with maxtab--
    cout << "Your binary number: ";

    while (tab>=0) //until we get to the 0 (1st) element of the table
    {
        cout << table[tab] << " "; //write the value of an element (0 or 1)
        tab--; //decreasing by 1 so we show 0's and 1's FROM THE BACK (correct way)
    }

    cout << endl;
    return 0;
}

By the way it's complicated but I tried my best.

edit - Here is the solution I ended up using:

std::string toBinary(int n)
{
    std::string r;
    while(n!=0) {r=(n%2==0 ?"0":"1")+r; n/=2;}
    return r;
}

std::bitset has a .to_string() method that returns a std::string holding a text representation in binary, with leading-zero padding.

Choose the width of the bitset as needed for your data, e.g. std::bitset<32> to get 32-character strings from 32-bit integers.

#include <iostream>
#include <bitset>

int main()
{
	std::string binary = std::bitset<8>(128).to_string(); //to binary
	std::cout<<binary<<"\n";
	
    unsigned long decimal = std::bitset<8>(binary).to_ulong();
    std::cout<<decimal<<"\n";
	return 0;
}

EDIT: Please do not edit my answer for Octal and Hexadecimal. The OP specifically asked for Decimal To Binary.

The following is a recursive function which takes a positive integer and prints its binary digits to the console.

Alex suggested, for efficiency, you may want to remove printf() and store the result in memory... depending on storage method result may be reversed.

/**
 * Takes a unsigned integer, converts it into binary and prints it to the console.
 * @param n the number to convert and print
 */
void convertToBinary(unsigned int n)
{
	if (n / 2 != 0) {
		convertToBinary(n / 2);
	}
	printf("%d", n % 2);
}

Credits to UoA ENGGEN 131

*Note: The benefit of using an unsigned int is that it can't be negative.

You can use std::bitset to convert a number to its binary format.

Use the following code snippet:

std::string binary = std::bitset<8>(n).to_string();

I found this on stackoverflow itself. I am attaching the link.

A pretty straight forward solution to print binary:

#include <iostream>
using namespace std;
int main()
{
 int num,arr[64];
 cin>>num;
 int i=0,r;
 while(num!=0)
{
  r = num%2;
  arr[i++] = r;
  num /= 2;
}

for(int j=i-1;j>=0;j--){
 cout<<arr[j];
  }
}

Non recursive solution:

#include <iostream>
#include<string>


std::string toBinary(int n)
{
    std::string r;
    while(n!=0) {r=(n%2==0 ?"0":"1")+r; n/=2;}
    return r;
}
int main()
{
    std::string i= toBinary(10);
    std::cout<<i;
}

Recursive solution:

#include <iostream>
#include<string>

std::string r="";
std::string toBinary(int n)
{
    r=(n%2==0 ?"0":"1")+r;
    if (n / 2 != 0) {
        toBinary(n / 2);
    }
    return r;
}
int main()
{
    std::string i=toBinary(10);
    std::cout<<i;
}

An int variable is not in decimal, it's in binary. What you're looking for is a binary string representation of the number, which you can get by applying a mask that filters individual bits, and then printing them:

for( int i = sizeof(value)*CHAR_BIT-1; i>=0; --i)
    cout << value & (1 << i) ? '1' : '0';

That's the solution if your question is algorithmic. If not, you should use the std::bitset class to handle this for you:

bitset< sizeof(value)*CHAR_BIT > bits( value );
cout << bits.to_string();

Here are two approaches. The one is similar to your approach

#include <iostream>
#include <string>
#include <limits>
#include <algorithm>

int main()
{
	while ( true )
	{
		std::cout << "Enter a non-negative number (0-exit): ";

		unsigned long long x = 0;
		std::cin >> x;

		if ( !x ) break;

		const unsigned long long base = 2;

		std::string s;
		s.reserve( std::numeric_limits<unsigned long long>::digits ); 

		do { s.push_back( x % base + '0' ); } while ( x /= base );

		std::cout << std::string( s.rbegin(), s.rend() )  << std::endl;
	}
}

and the other uses std::bitset as others suggested.

#include <iostream>
#include <string>
#include <bitset>
#include <limits>

int main()
{
	while ( true )
	{
		std::cout << "Enter a non-negative number (0-exit): ";

		unsigned long long x = 0;
		std::cin >> x;

		if ( !x ) break;

		std::string s = 
			std::bitset<std::numeric_limits<unsigned long long>::digits>( x ).to_string();

		std::string::size_type n = s.find( '1' ); 
		std::cout << s.substr( n )  << std::endl;
	}
}

The conversion from natural number to a binary string:

string toBinary(int n) {
	if (n==0) return "0";
	else if (n==1) return "1";
	else if (n%2 == 0) return toBinary(n/2) + "0";
	else if (n%2 != 0) return toBinary(n/2) + "1";
}

Here is modern variant that can be used for ints of different sizes.

#include <type_traits>
#include <bitset>

template<typename T>
std::enable_if_t<std::is_integral_v<T>,std::string>
encode_binary(T i){
    return std::bitset<sizeof(T) * 8>(i).to_string();
}

For this , In C++ you can use itoa() function .This function convert any Decimal integer to binary, decimal , hexadecimal and octal number.

#include<bits/stdc++.h>
using namespace std;
int main(){
 int a;    
 char res[1000];
 cin>>a;
 itoa(a,res,10);
 cout<<"Decimal- "<<res<<endl;
 itoa(a,res,2);
 cout<<"Binary- "<<res<<endl;
 itoa(a,res,16);
 cout<<"Hexadecimal- "<<res<<endl;
 itoa(a,res,8);
 cout<<"Octal- "<<res<<endl;return 0;
}

However, it is only supported by specific compilers.

You can see also: itoa - C++ Reference

Your solution needs a modification. The final string should be reversed before returning:

std::reverse(r.begin(), r.end());
return r;

DECIMAL TO BINARY NO ARRAYS USED *made by Oya:

I'm still a beginner, so this code will only use loops and variables xD...

Hope you like it. This can probably be made simpler than it is...

    #include <iostream>
    #include <cmath>
    #include <cstdlib>

    using namespace std;

    int main()
    {
        int i;
        int expoentes; //the sequence > pow(2,i) or 2^i
        int decimal; 
        int extra; //this will be used to add some 0s between the 1s
        int x = 1;

        cout << "\nThis program converts natural numbers into binary code\nPlease enter a Natural number:";
        cout << "\n\nWARNING: Only works until ~1.073 millions\n";
        cout << "     To exit, enter a negative number\n\n";

        while(decimal >= 0){
            cout << "\n----- // -----\n\n";
            cin >> decimal;
            cout << "\n";

            if(decimal == 0){
                cout << "0";
            }
            while(decimal >= 1){
                i = 0;
                expoentes = 1;
                while(decimal >= expoentes){
                    i++;
                    expoentes = pow(2,i);
                }
                x = 1;
                cout << "1";
                decimal -= pow(2,i-x);
                extra = pow(2,i-1-x);
                while(decimal < extra){
                    cout << "0";
                    x++;
                    extra = pow(2,i-1-x);
                }
            }
        }
        return 0;
    }

here a simple converter by using std::string as container. it allows a negative value.

#include <iostream>
#include <string>
#include <limits>

int main()
{
    int x = -14;

    int n = std::numeric_limits<int>::digits - 1;

    std::string s;
    s.reserve(n + 1);

    do
        s.push_back(((x >> n) & 1) + '0');
    while(--n > -1);

    std::cout << s << '\n';
}

This is a more simple program than ever

//Program to convert Decimal into Binary
#include<iostream>
using namespace std;
int main()
{
	long int dec;
    int rem,i,j,bin[100],count=-1;
    again:
    cout<<"ENTER THE DECIMAL NUMBER:- ";
    cin>>dec;//input of Decimal
    if(dec<0)
    {
	    cout<<"PLEASE ENTER A POSITIVE DECIMAL";
	    goto again;
    }
    else
	    {
	    cout<<"\nIT's BINARY FORM IS:- ";
	    for(i=0;dec!=0;i++)//making array of binary, but reversed
	    {
		    rem=dec%2;
		    bin[i]=rem;
		    dec=dec/2;
		    count++;
	    }
	    for(j=count;j>=0;j--)//reversed binary is printed in correct order
	    {
		    cout<<bin[j];
	    }
    }
    return 0; 
}

There is in fact a very simple way to do so. What we do is using a recursive function which is given the number (int) in the parameter. It is pretty easy to understand. You can add other conditions/variations too. Here is the code:

int binary(int num)
{
    int rem;
    if (num <= 1)
        {
            cout << num;
            return num;
        }
    rem = num % 2;
    binary(num / 2);
    cout << rem;
    return rem;
}

// function to convert decimal to binary
void decToBinary(int n)
{
    // array to store binary number
    int binaryNum[1000];
 
    // counter for binary array
    int i = 0;
    while (n > 0) {
 
        // storing remainder in binary array
        binaryNum[i] = n % 2;
        n = n / 2;
        i++;
    }
 
    // printing binary array in reverse order
    for (int j = i - 1; j >= 0; j--)
        cout << binaryNum[j];
}

refer :- https://www.geeksforgeeks.org/program-decimal-binary-conversion/

or using function :-

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

int main()
{
      
    int n;cin>>n;
    cout<<bitset<8>(n).to_string()<<endl;


}

or using left shift

#include<bits/stdc++.h>
using namespace std;
int main()
{
    // here n is the number of bit representation we want 
    int n;cin>>n;

    // num is a number whose binary representation we want
    int num;
    cin>>num;

    for(int i=n-1;i>=0;i--)
    {
        if( num & ( 1 << i ) ) cout<<1;
        else cout<<0;
    }


}

Below is simple C code that converts binary to decimal and back again. I wrote it long ago for a project in which the target was an embedded processor and the development tools had a stdlib that was way too big for the firmware ROM.

This is generic C code that does not use any library, nor does it use division or the remainder (%) operator (which is slow on some embedded processors), nor does it use any floating point, nor does it use any table lookup nor emulate any BCD arithmetic. What it does make use of is the type long long, more specifically unsigned long long (or uint64_t), so if your embedded processor (and the C compiler that goes with it) cannot do 64-bit integer arithmetic, this code is not for your application. Otherwise, I think this is production quality C code (maybe after changing long to int32_t and unsigned long long to uint64_t). I have run this overnight to test it for every 2³² signed integer values and there is no error in conversion in either direction.

We had a C compiler/linker that could generate executables and we needed to do what we could do without any stdlib (which was a pig). So no printf() nor scanf(). Not even an sprintf() nor sscanf(). But we still had a user interface and had to convert base-10 numbers into binary and back. (We also made up our own malloc()-like utility also and our own transcendental math functions too.)

So this was how I did it (the main program and calls to stdlib were there for testing this thing on my mac, not for the embedded code). Also, because some older dev systems don't recognize "int64_t" and "uint64_t" and similar types, the types long long and unsigned long long are used and assumed to be the same. And long is assumed to be 32 bits. I guess I could have typedefed it.

// returns an error code, 0 if no error,
// -1 if too big, -2 for other formatting errors
int decimal_to_binary(char *dec, long *bin)
    {
    int i = 0;
    
    int past_leading_space = 0;
    while (i <= 64 && !past_leading_space)        // first get past leading spaces
        {
        if (dec[i] == ' ')
            {
            i++;
            }
         else
            {
            past_leading_space = 1;
            }
        }
    if (!past_leading_space)
        {
        return -2;                                // 64 leading spaces does not a number make
        }
    // at this point the only legitimate remaining
    // chars are decimal digits or a leading plus or minus sign

    int negative = 0;
    if (dec[i] == '-')
        {
        negative = 1;
        i++;
        }
     else if (dec[i] == '+')
        {
        i++;                                    // do nothing but go on to next char
        }
    // now the only legitimate chars are decimal digits
    if (dec[i] == '\0')
        {
        return -2;                              // there needs to be at least one good 
        }                                       // digit before terminating string
    
    unsigned long abs_bin = 0;
    while (i <= 64 && dec[i] != '\0')
        {
        if ( dec[i] >= '0' && dec[i] <= '9' )
            {
            if (abs_bin > 214748364)
                {
                return -1;                                // this is going to be too big
                }
            abs_bin *= 10;                                // previous value gets bumped to the left one digit...                
            abs_bin += (unsigned long)(dec[i] - '0');     // ... and a new digit appended to the right
            i++;
            }
         else
            {
            return -2;                                    // not a legit digit in text string
            }
        }
    
    if (dec[i] != '\0')
        {
        return -2;                                // not terminated string in 64 chars
        }
    
    if (negative)
        {
        if (abs_bin > 2147483648)
            {
            return -1;                            // too big
            }
        *bin = -(long)abs_bin;
        }
     else
        {
        if (abs_bin > 2147483647)
            {
            return -1;                            // too big
            }
        *bin = (long)abs_bin;
        }
    
    return 0;
    }


void binary_to_decimal(char *dec, long bin)
    {
    unsigned long long acc;                // 64-bit unsigned integer
    
    if (bin < 0)
        {
        *(dec++) = '-';                    // leading minus sign
        bin = -bin;                        // make bin value positive
        }
    
    acc = 989312855LL*(unsigned long)bin;        // very nearly 0.2303423488 * 2^32
    acc += 0x00000000FFFFFFFFLL;                 // we need to round up
    acc >>= 32;
    acc += 57646075LL*(unsigned long)bin;
    // (2^59)/(10^10)  =  57646075.2303423488  =  57646075 + (989312854.979825)/(2^32)  
    
    int past_leading_zeros = 0;
    for (int i=9; i>=0; i--)            // maximum number of digits is 10
        {
        acc <<= 1;
        acc += (acc<<2);                // an efficient way to multiply a long long by 10
//      acc *= 10;
        
        unsigned int digit = (unsigned int)(acc >> 59);        // the digit we want is in bits 59 - 62
        
        if (digit > 0)
            {
            past_leading_zeros = 1;
            }
        
        if (past_leading_zeros)
            {
            *(dec++) = '0' + digit;
            }
        
        acc &= 0x07FFFFFFFFFFFFFFLL;    // mask off this digit and go on to the next digit
        }
    
    if (!past_leading_zeros)            // if all digits are zero ...
        {
        *(dec++) = '0';                 // ... put in at least one zero digit
        }
    
    *dec = '\0';                        // terminate string
    }


#if 1

#include <stdlib.h>
#include <stdio.h>
int main (int argc, const char* argv[])
    {
    char dec[64];
    long bin, result1, result2;
    unsigned long num_errors;
    long long long_long_bin;
    
    num_errors = 0;
    for (long_long_bin=-2147483648LL; long_long_bin<=2147483647LL; long_long_bin++)
        {
        bin = (long)long_long_bin;
        if ((bin&0x00FFFFFFL) == 0)
            {
            printf("bin = %ld \n", bin);        // this is to tell us that things are moving along
            }
        binary_to_decimal(dec, bin);
        decimal_to_binary(dec, &result1);
        sscanf(dec, "%ld", &result2);            // decimal_to_binary() should do the same as this sscanf()
        
        if (bin != result1 || bin != result2)
            {
            num_errors++;
            printf("bin = %ld, result1 = %ld, result2 = %ld, num_errors = %ld, dec = %s \n",
                bin, result1, result2, num_errors, dec);
            }
        }
    
    printf("num_errors = %ld \n", num_errors);
    
    return 0;
    }

#else

#include <stdlib.h>
#include <stdio.h>
int main (int argc, const char* argv[])
    {
    char dec[64];
    long bin;
    
    printf("bin = ");
    scanf("%ld", &bin);
    while (bin != 0)
        {
        binary_to_decimal(dec, bin);
        printf("dec = %s \n", dec);
        printf("bin = ");
        scanf("%ld", &bin);
        }
    
    return 0;
    }

#endif

#include <iostream>
#include <bitset>

#define bits(x)  (std::string( \
            std::bitset<8>(x).to_string<char,std::string::traits_type, std::string::allocator_type>() ).c_str() )


int main() {

   std::cout << bits( -86 >> 1 ) << ": " << (-86 >> 1) << std::endl;

   return 0;
}

Okay.. I might be a bit new to C++, but I feel the above examples don't quite get the job done right.

Here's my take on this situation.

char* DecimalToBinary(unsigned __int64 value, int bit_precision)
{
	int length = (bit_precision + 7) >> 3 << 3;
	static char* binary = new char[1 + length];
	int begin = length - bit_precision;
	unsigned __int64 bit_value = 1;
	for (int n = length; --n >= begin; )
	{
		binary[n] = 48 | ((value & bit_value) == bit_value);
		bit_value <<= 1;
	}
	for (int n = begin; --n >= 0; )
		binary[n] = 48;

	binary[length] = 0;
	return binary;
}

@value = The Value we are checking.

@bit_precision = The highest left most bit to check for.

@Length = The Maximum Byte Block Size. E.g. 7 = 1 Byte and 9 = 2 Byte, but we represent this in form of bits so 1 Byte = 8 Bits.

@binary = just some dumb name I gave to call the array of chars we are setting. We set this to static so it won't be recreated with every call. For simply getting a result and display it then this works good, but if let's say you wanted to display multiple results on a UI they would all show up as the last result. This can be fixed by removing static, but make sure you delete [] the results when you are done with it.

@begin = This is the lowest index that we are checking. Everything beyond this point is ignored. Or as shown in 2nd loop set to 0.

@first loop - Here we set the value to 48 and basically add a 0 or 1 to 48 based on the bool value of (value & bit_value) == bit_value. If this is true the char is set to 49. If this is false the char is set to 48. Then we shift the bit_value or basically multiply it by 2.

@second loop - Here we set all the indexes we ignored to 48 or '0'.

SOME EXAMPLE OUTPUTS!!!

int main()
{
	int val = -1;
	std::cout << DecimalToBinary(val, 1) << '\n';
	std::cout << DecimalToBinary(val, 3) << '\n';
	std::cout << DecimalToBinary(val, 7) << '\n';
	std::cout << DecimalToBinary(val, 33) << '\n';
	std::cout << DecimalToBinary(val, 64) << '\n';
	std::cout << "\nPress any key to continue. . .";
	std::cin.ignore();
	return 0;
}

00000001 //Value = 2^1 - 1
00000111 //Value = 2^3 - 1.
01111111 //Value = 2^7 - 1.
0000000111111111111111111111111111111111 //Value = 2^33 - 1.
1111111111111111111111111111111111111111111111111111111111111111 //Value = 2^64 - 1.

SPEED TESTS

Original Question's Answer: "Method: toBinary(int);"

Executions: 10,000 , Total Time (Milli): 4701.15 , Average Time (Nanoseconds): 470114

My Version: "Method: DecimalToBinary(int, int);"

//Using 64 Bit Precision.

Executions: 10,000,000 , Total Time (Milli): 3386 , Average Time (Nanoseconds): 338

//Using 1 Bit Precision.

Executions: 10,000,000, Total Time (Milli): 634, Average Time (Nanoseconds): 63

You want to do something like:

cout << "Enter a decimal number: ";
cin >> a1;
cout << setbase(2);
cout << a1

#include "stdafx.h"
#include<iostream>
#include<vector>
#include<cmath>

using namespace std;

int main() {
	// Initialize Variables
	double x;
	int xOct;
	int xHex;
	
	//Initialize a variable that stores the order if the numbers in binary/sexagesimal base
	vector<int> rem;

	//Get Demical value
	cout << "Number (demical base): ";
	cin >> x;
	
	//Set the variables
	xOct = x;
	xHex = x;

	//Get the binary value
	for (int i = 0; x >= 1; i++) {
		rem.push_back(abs(remainder(x, 2)));
		x = floor(x / 2);
	}
	
	//Print binary value
	cout << "Binary: ";
	int n = rem.size();
	while (n > 0) {
		n--;
		cout << rem[n];
	} cout << endl;

	//Print octal base
	cout << oct << "Octal: " << xOct << endl;

	//Print hexademical base
	cout << hex << "Hexademical: " << xHex << endl;

	system("pause");
	return 0;
}

#include <iostream>
using namespace std;
            
int main()
{  
    int a,b;
    cin>>a;
    for(int i=31;i>=0;i--)
    {
        b=(a>>i)&1;
        cout<<b;
    }
}

HOPE YOU LIKE THIS SIMPLE CODE OF CONVERSION FROM DECIMAL TO BINARY

  
  #include<iostream>
    using namespace std;
    int main()
    {
    	int input,rem,res,count=0,i=0;
    	cout<<"Input number: ";
    	cin>>input;`enter code here`
    	int num=input;
    	while(input > 0)
    	{
    		input=input/2;	
    		count++;
    	}
    	
    	int arr[count];
    	
    	while(num > 0)
    	{
    		arr[i]=num%2;
    		num=num/2;	
    		i++;
    	}
    	for(int i=count-1 ; i>=0 ; i--)
    	{
    		cout<<" " << arr[i]<<" ";
    	}
    	
    	
    	
    	return 0;
    }

SOLUTION 1

Shortest function. Recursive. No headers required.

size_t bin(int i) {return i<2?i:10*bin(i/2)+i%2;}

The simplicity of this function comes at the cost of some limitations. It returns correct values only for arguments between 0 and 1048575 (2 to the power of how many digits the largest unsigned int has, -1). I used the following program to test it:

#include <iostream> // std::cout, std::cin
#include <climits>  // ULLONG_MAX
#include <math.h>   // pow()
int main()
{
    size_t bin(int);
    int digits(size_t);
    int i = digits(ULLONG_MAX); // maximum digits of the return value of bin()
    int iMax = pow(2.0,i)-1;    // maximum value of a valid argument of bin()
    while(true) {
        std::cout << "Decimal: ";
        std::cin >> i;
        if (i<0 or i>iMax) {
            std::cout << "\nB Integer out of range, 12:1";
            return 0;
        }
        std::cout << "Binary:  " << bin(i) << "\n\n";
    }
    return 0;
}

size_t bin(int i) {return i<2?i:10*bin(i/2)+i%2;}
int digits(size_t i) {return i<10?1:digits(i/10)+1;}

SOLUTION 2

Short. Recursive. Some headers required.

std::string bin(size_t i){return !i?"0":i==1?"1":bin(i/2)+(i%2?'1':'0');}

This function can return the binary representation of the largest integers as a string. I used the following program to test it:

#include <string>   // std::string
#include <iostream> // std::cout, std::cin

int main()
{
    std::string s, bin(size_t);
    size_t i, x;
    std::cout << "Enter exit code: "; // Used to exit the program.
    std::cin >> x;
    while(i!=x) {
        std::cout << "\nDecimal: ";
        std::cin >> i;
        std::cout << "Binary:  " << bin(i) << "\n";
    }
    return 0;
}

std::string bin(size_t i){return !i?"0":i==1?"1":bin(i/2)+(i%2?'1':'0');}

My way of converting decimal to binary in C++. But since we are using mod, this function will work in case of hexadecimal or octal also. You can also specify bits. This function keeps calculating the lowest significant bit and place it on the end of the string. If you are not so similar to this method than you can vist: <https://www.wikihow.com/Convert-from-Decimal-to-Binary>

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

string itob(int bits, int n) {
  int count;

  char str[bits + 1];  // +1 to append NULL character.

  str[bits] = '\0';    // The NULL character in a character array flags the end
                       // of the string, not appending it may cause problems.

  count = bits - 1;    // If the length of a string is n, than the index of the
                       // last character of the string will be n - 1. Cause the
                       // index is 0 based not 1 based. Try yourself.

  do {
    if (n % 2)
      str[count] = '1';
    else
      str[count] = '0';
    n /= 2;
    count--;
  } while (n > 0);

  while (count > -1) {
    str[count] = '0';
    count--;
  }

  return str;
}

int main() {
  cout << itob(1, 0) << endl;    // 0 in 1 bit binary.
  cout << itob(2, 1) << endl;    // 1 in 2 bit binary.
  cout << itob(3, 2) << endl;    // 2 in 3 bit binary.
  cout << itob(4, 4) << endl;    // 4 in 4 bit binary.
  cout << itob(5, 15) << endl;   // 15 in 5 bit binary.
  cout << itob(6, 30) << endl;   // 30 in 6 bit binary.
  cout << itob(7, 61) << endl;   // 61 in 7 bit binary.
  cout << itob(8, 127) << endl;  // 127 in 8 bit binary.
  return 0;
}

The Output:

0
01
010
0100
01111
011110
0111101
01111111

#include <iostream>
 
// x is our number to test
// pow is a power of 2 (e.g. 128, 64, 32, etc...)
int printandDecrementBit(int x, int pow)
{
    // Test whether our x is greater than some power of 2 and print the bit
    if (x >= pow)
    {
        std::cout << "1";
        // If x is greater than our power of 2, subtract the power of 2
        return x - pow;
    }
    else
    {
        std::cout << "0";
        return x;
    }
}
 
int main()
{
    std::cout << "Enter an integer between 0 and 255: ";
    int x;
    std::cin >> x;
 
    x = printandDecrementBit(x, 128);
    x = printandDecrementBit(x, 64);
    x = printandDecrementBit(x, 32);
    x = printandDecrementBit(x, 16);
 
    std::cout << " ";
 
    x = printandDecrementBit(x, 8);
    x = printandDecrementBit(x, 4);
    x = printandDecrementBit(x, 2);
    x = printandDecrementBit(x, 1);
 
    return 0;
}

this is a simple way to get the binary form of an int. credit to learncpp.com. im sure this could be used in different ways to get to the same point.

In this approach, the decimal will be converted to the respective binary number in the string formate. The string return type is chosen since it can handle more range of input values.

class Solution {
public:
  string ConvertToBinary(int num) 
  {
    vector<int> bin;
    string op;
    for (int i = 0; num > 0; i++)
    {
      bin.push_back(num % 2);
      num /= 2;
    }
    reverse(bin.begin(), bin.end());
    for (size_t i = 0; i < bin.size(); ++i)
    {
      op += to_string(bin[i]);
    }
    return op;
  }
};

using bitmask and bitwise and .

string int2bin(int n){
	string x;
	for(int i=0;i<32;i++){
		if(n&1) {x+='1';}
		else {x+='0';}
		n>>=1;
	}
	reverse(x.begin(),x.end());
	return x;
}

You Could use std::bitset:

#include <bits/stdc++.h>

int main()
{
    std::string binary = std::bitset<(int)ceil(log2(10))>(10).to_string(); // decimal number is 10
    std::cout << binary << std::endl; // 1010
    return 0;
}

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

void Decimal2Binary(long value,char *b,int len)
{
    if(value>0)
    {
        do
        {
            if(value==1)
            {
                *(b+len-1)='1';
                break;
            }
            else
            {
                *(b+len-1)=(value%2)+48;
                value=value/2;
                len--;
            }
        }while(1);
    }
}
long Binary2Decimal(char *b,int len)
{
    int i=0;
    int j=0;
    long value=0;
    for(i=(len-1);i>=0;i--)
    {
        if(*(b+i)==49)
        {
            value+=pow(2,j);
        }
        j++;
    }
    return value;
}
int main()
{
    char data[11];//最後一個BIT要拿來當字串結尾
    long value=1023;
    memset(data,'0',sizeof(data));
    data[10]='\0';//字串結尾
    Decimal2Binary(value,data,10);
    printf("%d->%s\n",value,data);
    value=Binary2Decimal(data,10);
    printf("%s->%d",data,value);
    return 0;
}