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

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Updated on 28 Jan 2022

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