C++. See binary, hex, octal, and decimal representations of a number.

decimal-converter.cpp

// Include headers for classes...
#include <iostream>
#include <iomanip>
#include <string>
#include <bitset>

// Classes from different namespaces...
using std::cout;
using std::cin;
using std::endl;

// Namespace containing utility functions for formatting numbers
namespace numutil {
    // Using statements for convenient access to certain functions
    using std::setw;
    using std::setfill;
    using std::oct;
    using std::hex;
    using std::bitset;
    using std::to_string;
    using std::uppercase;

    // Prints the decimal representation of a number to the console
    void printInDecimal(int num) {
        cout << "Decimal: " << num << endl;
    }

    // Prints the octal representation of a number to the console
    void printInOctal(int num) {
        // Determine the minimum width needed for the output, so single digit numbers display correctly eg: 9 is displayed as 09.
        int width = to_string(num).length(); // get length of the int
        if (width == 1)
        {
            width++; // pad with an extra zero becauses its a single digit
        }
        // Use the octal manipulator and set the width and fill character for output
        cout << "Octal: " << oct << setw(width + 1) << setfill('0') << num << endl;
    }

    // Prints the hexadecimal representation of a number to the console
    void printInHexadecimal(int num) {
        // Use the hexadecimal manipulator and set the width, fill character, and uppercase flag for output
        cout << "Hexadecimal: " << "0x"<< uppercase << hex << setw(8) << setfill('0') << num << endl;
    }
    // Prints the binary representation of a number to the console
    void printInBinary(int num) {
        // The sizeof operator returns the size of the num variable in bytes, so we multiply by 8 to get the size in bits
        cout << "Binary: " << bitset<sizeof(num)*8>(num) << endl;
    }
}

// Main function...
int main() {
    int num;

    // Get input from user...
    cout << "Enter a number: ";
    cin >> num;

    // Call the utility functions to print the number in different formats
    numutil::printInDecimal(num);
    numutil::printInOctal(num);
    numutil::printInHexadecimal(num);
    numutil::printInBinary(num);

    return 0;
}