C++ program to convert a hexadecimal value to binary

C++ program to convert a hexadecimal value to binary:

In this post, we will learn how to convert a hexadecimal value to binary in C++. The program will take a hexadecimal value as input from the user, convert it to binary and print that.

Hexadecimal and binary number system:

Hexadecimal and binary, both are different number systems. The hexadecimal number system uses 16 as the base. For decimal numbers 0 to 9, hexadecimal uses 0 to 9. For 10 to 15, it uses A to F. We can also use a to f. We have to use letters because we need to represent all two digit numbers using one character.

The binary number system uses 2 as base. So, all numbers are represented in 0 and 1 in the binary system.

Algorithm:

We will use the below algorithm to convert a hexadecimal value to binary:

  • Get the hexadecimal value as an input from the user.
  • For each character of the hexadecimal value, convert it to binary.
  • Join all binary values to get the final binary result.

For example, if we want to convert 2A9B to binary,

  • Binary equivalent of 2 is 0010
  • Binary equivalent of A is 1010
  • Binary equivalent of 9 is 1001
  • Binary equivalent of B is 1011

So, the binary of 2A9B is 0010101010011011.

  • The program will iterate through the characters of the hexadecimal string one by one.
  • It will initialize a result string as an empty string to hold the final binary conversion.
  • It will use a loop to iterate through the characters of the string one by one. For each character, it will find the binary equivalent and add it to the result string.

C++ program:

Below is the complete C++ program:

#include <iostream>
#include <string>

using namespace std;

string getBinary(char c)
{
	switch (c)
	{
	case '0':
		return "0000";
	case '1':
		return "0001";

	case '2':
		return "0010";

	case '3':
		return "0011";

	case '4':
		return "0100";

	case '5':
		return "0101";

	case '6':
		return "0110";

	case '7':
		return "0111";

	case '8':
		return "1000";

	case '9':
		return "1001";

	case 'A':
	case 'a':
		return "1010";

	case 'B':
	case 'b':
		return "1011";

	case 'C':
	case 'c':
		return "1100";

	case 'D':
	case 'd':
		return "1101";

	case 'E':
	case 'e':
		return "1110";

	case 'F':
	case 'f':
		return "1111";
	default:
		return "-1";
	}
}

int main()
{
	string hexString;
	string binaryString = "";

	cout << "Enter the hexadecimal string: " << endl;
	cin >> hexString;

	for (int i = 0; i < hexString.length(); i++)
	{
		binaryString += getBinary(hexString[i]);
	}

	cout << "Binary: " << binaryString << endl;

	return 0;
}

Here,

  • getBinary is a method to get the binary string for a given character. It takes a character as its parameter and returns the binary equivalent.

    • It uses a switch-case block. We have defined the binary equivalent of all possible hexadecimal characters.
  • hexString variable is initialized to hold the hexadecimal string and binaryString is to hold the final binary string. binaryString is initialized as an empty string.
  • It asks the user to enter the hexadecimal string and reads the string to the hexString variable.
  • The for loop iterates through the characters of the hexadecimal string one by one.

    • For each character, it finds the binary equivalent by calling the getBinary method.
    • It appends the binary string to the end of binaryString.
  • At the end of the program, it prints the binary string binaryString to the user.

If you run this program, it will give output as like below:

Enter the hexadecimal string: 
2a9b
Binary: 0010101010011011

It will work for all valid hexadecimal strings. But, it will not show any error message for invalid strings. For example,

Enter the hexadecimal string: 
2ty
Binary: 0010-1-1

This is because, the getBinary method returns -1 for invalid hexadecimal characters and we don’t have any checks for invalid characters.

Method 2: Handle invalid hexadecimal inputs:

Let’s change the above method a little bit to handle invalid hexadecimal inputs:

#include <iostream>
#include <string>

using namespace std;

string getBinary(char c)
{
	switch (c)
	{
	case '0':
		return "0000";
	case '1':
		return "0001";

	case '2':
		return "0010";

	case '3':
		return "0011";

	case '4':
		return "0100";

	case '5':
		return "0101";

	case '6':
		return "0110";

	case '7':
		return "0111";

	case '8':
		return "1000";

	case '9':
		return "1001";

	case 'A':
	case 'a':
		return "1010";

	case 'B':
	case 'b':
		return "1011";

	case 'C':
	case 'c':
		return "1100";

	case 'D':
	case 'd':
		return "1101";

	case 'E':
	case 'e':
		return "1110";

	case 'F':
	case 'f':
		return "1111";
	default:
		return "-1";
	}
}

int main()
{
	string hexString;
	string binaryString = "";

	bool isValid = true;
	string binary;

	cout << "Enter the hexadecimal string: " << endl;
	cin >> hexString;

	for (int i = 0; i < hexString.length(); i++)
	{
		binary = getBinary(hexString[i]);
		if (binary == "-1")
		{
			isValid = false;
			break;
		}
		binaryString += binary;
	}

	if (isValid)
	{
		cout << "Binary: " << binaryString << endl;
	}
	else
	{
		cout << "Invalid hexadecimal input" << endl;
	}

	return 0;
}

Following are the changes I did for this program:

  • One boolean value isValid is initialized as true. This variable defines if the input is a valid input or not.
  • Another string variable binary is initialized to hold the binary value for a hexadecimal character.
  • Inside the for loop, the return value of getBinary is stored in the binary variable first before appending to binaryString. If the value of binary is -1, i.e. if any character in the hexadecimal string is invalid, it assigns false to isValid and exits from the loop.
  • After the for loop is completed, it checks the value of isValid and prints a message based on that.

It will give outputs as like below:

Enter the hexadecimal string: 
2ae7
Binary: 0010101011100111

Enter the hexadecimal string: 
uj9
Invalid hexadecimal input

C++ hexadecimal to binary example

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