C++ Program to Convert Decimal to Binary (Using Bitwise Operator, Array, Function, and Recursion)

Introduction

This article demonstrates how to write a C++ program to convert a decimal number to binary, using various techniques:

• Bitwise operator

• Without array

• With function

• With array

• Using recursion

Each version is fully explained with step-by-step code and a clean explanation section.

 

1. C++ Program to Convert Decimal to Binary Using Bitwise Operator

// C++ program to convert decimal to binary using bitwise operator
#include <iostream>
using namespace std;

// The main function of the program
int main()
{
    // Step-1 Declare variables
    int num;

    // Step-2 Input decimal number
    cout << "Enter a decimal number: ";
    cin >> num;

    // Step-3 Display binary using bitwise operator
    cout << "Binary representation: ";
    for (int i = 31; i >= 0; i--) {
        int bit = (num >> i) & 1;
        cout << bit;
    }

    cout << endl;
    return 0;
}

Run

Output

 

Explanation of the Code:

• Declare Variables: We declare an integer variable num to store the input.

• Input Value: Take user input using cin.

• Bitwise Operation: Use right shift (>>) and bitwise AND (& 1) to extract each bit from left to right (31 to 0).

• Output: Print all bits one after the other to form the binary number.

 

2. C++ Program to Convert Decimal to Binary Without Using Array

// C++ program to convert decimal to binary without using array
#include <iostream>
using namespace std;

// The main function of the program
int main()
{
    // Step-1 Declare variables
    int num;
    long long binary = 0;
    int place = 1;

    // Step-2 Input decimal number
    cout << "Enter a decimal number: ";
    cin >> num;

    // Step-3 Convert to binary without using array
    while (num != 0) {
        int remainder = num % 2;
        binary += remainder * place;
        num /= 2;
        place *= 10;
    }

    // Step-4 Output the binary number
    cout << "Binary representation: " << binary << endl;

    return 0;
}

Run

Output

 

Explanation of the Code:

• Declare Variables: num, binary, and place are initialized.

• Input Value: Decimal number is input via cin.

• Conversion Logic: Using modulus and division, we generate binary digits and build the result by multiplying with place value.

• Output: Print the final binary number using cout.

 

3. C++ Program to Convert Decimal to Binary Using Function

// C++ program to convert decimal to binary using function
#include <iostream>
using namespace std;

// Function to convert decimal to binary
long long convertToBinary(int num)
{
    long long binary = 0;
    int place = 1;

    // Convert to binary using mathematical logic
    while (num != 0) {
        int remainder = num % 2;
        binary += remainder * place;
        num /= 2;
        place *= 10;
    }

    return binary;
}

// The main function of the program
int main()
{
    // Step-1 Declare variables
    int number;

    // Step-2 Input decimal number
    cout << "Enter a decimal number: ";
    cin >> number;

    // Step-3 Call the function to convert
    long long result = convertToBinary(number);

    // Step-4 Output the result
    cout << "Binary representation: " << result << endl;

    return 0;
}

Run

Output

 

Explanation of the Code:

• Declare Variables: number is the input; result is the returned binary number.

• Function Use: convertToBinary() handles conversion logic.

• Separation of Logic: This approach follows good coding practice by separating logic and input/output.

• Output: Print the result returned by the function.

 

4. C++ Program to Convert Decimal to Binary Using Array

// C++ program to convert decimal to binary using array
#include <iostream>
using namespace std;

// The main function of the program
int main()
{
    // Step-1 Declare variables
    int num, binary[32], index = 0;

    // Step-2 Input decimal number
    cout << "Enter a decimal number: ";
    cin >> num;

    // Step-3 Convert decimal to binary using array
    while (num != 0) {
        binary[index++] = num % 2;
        num /= 2;
    }

    // Step-4 Output the binary number in reverse
    cout << "Binary representation: ";
    for (int i = index - 1; i >= 0; i--) {
        cout << binary[i];
    }

    cout << endl;
    return 0;
}

Run

Output

 

Explanation of the Code:

• Declare Array: binary[32] stores up to 32 binary digits.

• Conversion Logic: Digits are stored starting from least significant, so output is printed in reverse.

• Simple Looping: Division by 2 and storing remainders is the core logic.

• Output: Loop through the array in reverse to print binary digits.

 

5. C++ Program to Convert Decimal to Binary Using Recursion

// C++ program to convert decimal to binary using recursion
#include <iostream>
using namespace std;

// Recursive function to convert and print binary
void convertToBinary(int num)
{
    if (num == 0)
        return;

    // Recursive call
    convertToBinary(num / 2);

    // Print remainder
    cout << (num % 2);
}

// The main function of the program
int main()
{
    // Step-1 Declare variable
    int num;

    // Step-2 Input decimal number
    cout << "Enter a decimal number: ";
    cin >> num;

    // Step-3 Print binary using recursion
    cout << "Binary representation: ";
    if (num == 0)
        cout << "0";
    else
        convertToBinary(num);

    cout << endl;
    return 0;
}

Run

Output

 

Explanation of the Code:

• Recursive Approach: Function calls itself with num / 2 until num becomes 0.

• Print on Return: Digits are printed during function return (unwinding phase).

• Handles Edge Case: If num == 0, output is printed as 0.

• Elegant Solution: This is a clean and concise recursive approach to decimal to binary conversion in C++.

 

6. C++ Program to Convert Decimal to Binary Using std::bitset (Header Utility Method)

// C++ program to convert decimal to binary using bitset
#include <iostream>
#include <bitset>  // Required for bitset
using namespace std;

// The main function of the program
int main()
{
    // Step-1 Declare variable
    int num;

    // Step-2 Input decimal number
    cout << "Enter a decimal number: ";
    cin >> num;

    // Step-3 Use bitset to convert and print binary
    cout << "Binary representation: " << bitset<32>(num) << endl;

    return 0;
}

Run

Output

 

Explanation of the Code:

• Use of bitset: C++ STL's bitset<32> is used to directly convert and print binary for a 32-bit integer.

• No Manual Logic Needed: This method is the easiest if the full-length binary is needed.

• Useful for Fixed Width Representation: Often used in system-level programming.

 

7. C++ Program to Convert Decimal to Binary Using String Concatenation

// C++ program to convert decimal to binary using string
#include <iostream>
#include <string>
using namespace std;

// The main function of the program
int main()
{
    // Step-1 Declare variables
    int num;
    string binary = "";

    // Step-2 Input decimal number
    cout << "Enter a decimal number: ";
    cin >> num;

    // Step-3 Convert using string operations
    if (num == 0)
        binary = "0";
    else {
        while (num > 0) {
            binary = to_string(num % 2) + binary;
            num /= 2;
        }
    }

    // Step-4 Output the result
    cout << "Binary representation: " << binary << endl;

    return 0;
}

Run

Output

 

Explanation of the Code:

• String Building: Each digit is prepended to the string.

• Avoids Arrays or Recursion: Uses std::string instead.

• Readable and Efficient for Small Inputs: Especially in beginner projects.

 

8. C++ Program to Convert Decimal to Binary Using Stack (Reverse Order)

// C++ program to convert decimal to binary using stack
#include <iostream>
#include <stack>
using namespace std;

// The main function of the program
int main()
{
    // Step-1 Declare variables
    int num;
    stack<int> binaryStack;

    // Step-2 Input decimal number
    cout << "Enter a decimal number: ";
    cin >> num;

    // Step-3 Convert using stack to reverse bits
    if (num == 0) {
        cout << "Binary representation: 0\n";
        return 0;
    }

    while (num > 0) {
        binaryStack.push(num % 2);
        num /= 2;
    }

    // Step-4 Output binary from stack
    cout << "Binary representation: ";
    while (!binaryStack.empty()) {
        cout << binaryStack.top();
        binaryStack.pop();
    }

    cout << endl;
    return 0;
}

Run

Output

 

Explanation of the Code:

• Stack for Reversal: Binary digits are pushed in order and popped to print in reverse.

• Data Structure Use: This approach helps explain how stacks work.

• Educational Use: Great for beginners learning both stacks and binary conversion.