Program for Hexadecimal to Decimal
Last Updated :
03 Apr, 2025
Given a hexadecimal number as input, we need to write a program to convert the given hexadecimal number into an equivalent decimal number.
Examples:
Input : 67
Output: 103
Input : 512
Output: 1298
Input : 123
Output: 291
Hexadecimal Number
We know that hexadecimal number uses 16 symbols {0, 1, 2, 4, 5, 6, 7, 8, 9, A, B, C, D, E, F} to represent all numbers. Here, (A, B, C, D, E, F) represents (10, 11, 12, 13, 14, 15).
The idea is to extract the digits of a given hexadecimal number starting from the rightmost digit and keep a variable dec_value. At the time of extracting digits from the hexadecimal number, multiply the digit with the proper base (Power of 16) and add it to the variable dec_value. In the end, the variable dec_value will store the required decimal number.
For Example: If the hexadecimal number is 1A.
dec_value = 1*(161) + 10*(160) = 26
Decimal Number
The number which can be represented using the numbers in the range of (0-9) are termed as decimal number which has the base 10 to it.
For example, The number 123 is a decimal number where:
- 1 represents 100 (10²),
- 2 represents 20 (10¹),
- 3 represents 3 (10⁰).
Thus, 123 = 1×100 + 2×10 + 3×1.
The below diagram explains how to convert a hexadecimal number (1AB) to an equivalent decimal value:
Below is the implementation of the above idea.
C++
// C++ program to convert hexadecimal to decimal
#include <bits/stdc++.h>
using namespace std;
// Function to convert hexadecimal to decimal
int hexadecimalToDecimal(string hexVal)
{
int len = hexVal.size();
// Initializing base value to 1, i.e 16^0
int base = 1;
int dec_val = 0;
// Extracting characters as digits from last
// character
for (int i = len - 1; i >= 0; i--) {
// if character lies in '0'-'9', converting
// it to integral 0-9 by subtracting 48 from
// ASCII value
if (hexVal[i] >= '0' && hexVal[i] <= '9') {
dec_val += (int(hexVal[i]) - 48) * base;
// incrementing base by power
base = base * 16;
}
// if character lies in 'A'-'F' , converting
// it to integral 10 - 15 by subtracting 55
// from ASCII value
else if (hexVal[i] >= 'A' && hexVal[i] <= 'F') {
dec_val += (int(hexVal[i]) - 55) * base;
// incrementing base by power
base = base * 16;
}
}
return dec_val;
}
// driver program
int main()
{
string hexNum = "1A";
cout << (hexadecimalToDecimal(hexNum));
// This code is contributed by rakeshsahni
return 0;
}
// Java program to convert hexadecimal to decimal
import java.io.*;
class GFG {
// Function to convert hexadecimal to decimal
static int hexadecimalToDecimal(String hexVal)
{
int len = hexVal.length();
// Initializing base value to 1, i.e 16^0
int base = 1;
int dec_val = 0;
// Extracting characters as digits from last
// character
for (int i = len - 1; i >= 0; i--) {
// if character lies in '0'-'9', converting
// it to integral 0-9 by subtracting 48 from
// ASCII value
if (hexVal.charAt(i) >= '0'
&& hexVal.charAt(i) <= '9') {
dec_val += (hexVal.charAt(i) - 48) * base;
// incrementing base by power
base = base * 16;
}
// if character lies in 'A'-'F' , converting
// it to integral 10 - 15 by subtracting 55
// from ASCII value
else if (hexVal.charAt(i) >= 'A'
&& hexVal.charAt(i) <= 'F') {
dec_val += (hexVal.charAt(i) - 55) * base;
// incrementing base by power
base = base * 16;
}
}
return dec_val;
}
// driver program
public static void main(String[] args)
{
String hexNum = "1A";
System.out.println(hexadecimalToDecimal(hexNum));
}
}
# Python3 program to convert
# hexadecimal to decimal
# Function to convert hexadecimal
# to decimal
def hexadecimalToDecimal(hexval):
# Finding length
length = len(hexval)
# Initialize base value to 1,
# i.e. 16*0
base = 1
dec_val = 0
# Extracting characters as digits
# from last character
for i in range(length - 1, -1, -1):
# If character lies in '0'-'9',
# converting it to integral 0-9
# by subtracting 48 from ASCII value
if hexval[i] >= '0' and hexval[i] <= '9':
dec_val += (ord(hexval[i]) - 48) * base
# Incrementing base by power
base = base * 16
# If character lies in 'A'-'F',converting
# it to integral 10-15 by subtracting 55
# from ASCII value
elif hexval[i] >= 'A' and hexval[i] <= 'F':
dec_val += (ord(hexval[i]) - 55) * base
# Incrementing base by power
base = base * 16
return dec_val
# Driver code
if __name__ == '__main__':
hexnum = '1A'
print(hexadecimalToDecimal(hexnum))
# This code is contributed by virusbuddah_
// C# program to convert
// hexadecimal to decimal
using System;
class GFG {
// Function to convert
// hexadecimal to decimal
static int hexadecimalToDecimal(String hexVal)
{
int len = hexVal.Length;
// Initializing base1 value
// to 1, i.e 16^0
int base1 = 1;
int dec_val = 0;
// Extracting characters as
// digits from last character
for (int i = len - 1; i >= 0; i--) {
// if character lies in '0'-'9',
// converting it to integral 0-9
// by subtracting 48 from ASCII value
if (hexVal[i] >= '0' && hexVal[i] <= '9') {
dec_val += (hexVal[i] - 48) * base1;
// incrementing base1 by power
base1 = base1 * 16;
}
// if character lies in 'A'-'F' ,
// converting it to integral
// 10 - 15 by subtracting 55
// from ASCII value
else if (hexVal[i] >= 'A' && hexVal[i] <= 'F') {
dec_val += (hexVal[i] - 55) * base1;
// incrementing base1 by power
base1 = base1 * 16;
}
}
return dec_val;
}
// Driver Code
static void Main()
{
String hexNum = "1A";
Console.WriteLine(hexadecimalToDecimal(hexNum));
}
}
// This code is contributed by mits
<script>
// javascript program to convert hexadecimal to decimal
// Function to convert hexadecimal to decimal
function hexadecimalToDecimal(hexVal)
{
var len = hexVal.length;
// Initializing base value to 1, i.e 16^0
var base = 1;
var dec_val = 0;
// Extracting characters as digits from last
// character
for (var i = len - 1; i >= 0; i--) {
// if character lies in '0'-'9', converting
// it to integral 0-9 by subtracting 48 from
// ASCII value
if (hexVal.charAt(i) >= '0'
&& hexVal.charAt(i) <= '9') {
dec_val += (hexVal.charAt(i).charCodeAt(0) - 48) * base;
// incrementing base by power
base = base * 16;
}
// if character lies in 'A'-'F' , converting
// it to integral 10 - 15 by subtracting 55
// from ASCII value
else if (hexVal.charAt(i) >= 'A'
&& hexVal.charAt(i) <= 'F') {
dec_val += (hexVal.charAt(i).charCodeAt(0) - 55) * base;
// incrementing base by power
base = base * 16;
}
}
return dec_val;
}
// driver program
var hexNum = "1A";
document.write(hexadecimalToDecimal(hexNum));
// This code is contributed by 29AjayKumar
</script>
<?php
// PHP program to convert
// hexadecimal to decimal
// Function to convert
// hexadecimal to decimal
function hexadecimalToDecimal($hexVal)
{
$len = strlen($hexVal);
// Initializing base value
// to 1, i.e 16^0
$base = 1;
$dec_val = 0;
// Extracting characters as
// digits from last character
for ($i = $len - 1; $i >= 0; $i--)
{
// if character lies in '0'-'9',
// converting it to integral 0-9
// by subtracting 48 from ASCII value.
if ($hexVal[$i] >= '0' &&
$hexVal[$i] <= '9')
{
$dec_val += (ord($hexVal[$i]) - 48) *
$base;
// incrementing base by power
$base = $base * 16;
}
// if character lies in 'A'-'F' ,
// converting it to integral
// 10 - 15 by subtracting 55
// from ASCII value
else if ($hexVal[$i] >= 'A' &&
$hexVal[$i] <= 'F')
{
$dec_val += (ord($hexVal[$i]) - 55) *
$base;
// incrementing base by power
$base = $base * 16;
}
}
return $dec_val;
}
// Driver Code
$hexNum = "1A";
echo hexadecimalToDecimal($hexNum);
// This code is contributed by mits
?>
Time Complexity: O(N), where N is the number of digits in the given hexadecimal number.
Space Complexity: O(1).
Using predefined function
C++
// C++ program to convert octal to decimal
#include <bits/stdc++.h>
using namespace std;
int HexToDec(string n) { return stoi(n, 0, 16); }
int main()
{
string n = "1A";
cout << HexToDec(n);
return 0;
}
// This code is contributed by rakeshsahni
// Java program to convert hexadecimal to decimal
import java.io.*;
class GFG {
public static int HexToDec(String n)
{
return Integer.parseInt(n, 16);
}
public static void main(String[] args)
{
String n = "1A";
System.out.println(HexToDec(n));
}
}
# Python program to convert hexadecimal to decimal
def HexToDec(n):
return int(n, 16);
if __name__ == '__main__':
n = "1A";
print(HexToDec(n));
# This code is contributed by 29AjayKumar
// C# program to convert hexadecimal to decimal
using System;
public class GFG {
public static int HexToDec(String n)
{
return Convert.ToInt32(n, 16);
}
public static void Main(String[] args)
{
String n = "1A";
Console.WriteLine(HexToDec(n));
}
}
// This code is contributed by Amit Katiyar
<script>
// javascript program to convert octal to decimal
function HexToDec(n)
{
return parseInt(n, 16);
}
var n = "1A";
document.write(HexToDec(n));
// This code is contributed by 29AjayKumar
</script>
Time complexity: O(1) - the conversion of hexadecimal to decimal is done in constant time using the stoi function.
Auxiliary Space: O(1) - the only space used is for the string n and the returned integer value, which are constant in size regardless of the input value.
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