C++ Exercises: Convert a hexadecimal number to decimal number

Last update on August 14 2025 12:54:55 (UTC/GMT +8 hours)

79. Hexadecimal to Decimal Conversion

Write a C++ program to convert a hexadecimal number to a decimal number.

Visual Presentation:

C++ Exercises: Convert a hexadecimal number to decimal number

Sample Solution:-

C++ Code :

#include<iostream> // Include necessary libraries
#include<stdlib.h>
#include<math.h>
using namespace std; // Use the standard namespace

// Function to convert hexadecimal to decimal
unsigned long Hex_To_Dec(char hex[]) {
    char *hexstring; // Pointer to the hexadecimal string
    int length = 0; // Variable to store the length of the input string
    const int hexbase = 16; // Constant to define base 16 for hexadecimal
    unsigned long dnum = 0; // Variable to store the resulting decimal number
    int i;

    // Loop to calculate the length of the hexadecimal string
    for (hexstring = hex; *hexstring != '\0'; hexstring++) {
        length++;
    }

    hexstring = hex; // Reset the pointer to the start of the hexadecimal string

    // Loop to convert each character of the hexadecimal string to decimal
    for (i = 0; *hexstring != '\0' && i < length; i++, hexstring++) {
        if (*hexstring >= 48 && *hexstring <= 57) {  
            // Convert character to decimal if it's a number (0-9)
            dnum += (((int)(*hexstring)) - 48) * pow(hexbase, length - i - 1);
        }
        else if ((*hexstring >= 65 && *hexstring <= 70)) {  
            // Convert character to decimal if it's an uppercase letter (A-F)
            dnum += (((int)(*hexstring)) - 55) * pow(hexbase, length - i - 1);
        }
        else if (*hexstring >= 97 && *hexstring <= 102) {  
            // Convert character to decimal if it's a lowercase letter (a-f)
            dnum += (((int)(*hexstring)) - 87) * pow(hexbase, length - i - 1);
        }
        else {
            // Display an error message for an invalid input character
            cout << " The given hexadecimal number is invalid. \n";
        }
    }

    return dnum; // Return the resulting decimal number
}

// Main function
int main() {
    unsigned long dnum; // Variable to store the decimal number
    char hex[9]; // Array to store the input hexadecimal number

    cout << "\n\n Convert any hexadecimal number to decimal number:\n"; // Display purpose of the program
    cout << "------------------------------------------------------\n"; // Display separator line
    cout << " Input any 32-bit Hexadecimal Number: ";  
    cin >> hex; // Read the hexadecimal input from the user

    dnum = Hex_To_Dec(hex); // Call the function to convert hexadecimal to decimal

    cout << " The value in decimal number is: " << dnum << "\n"; // Display the resulting decimal number
}

Sample Output:

 Convert any hexadecimal number to decimal number:                     
------------------------------------------------------                 
 Input any 32-bit Hexadecimal Number: 25                               
 The value in decimal number is: 37

Flowchart:

For more Practice: Solve these Related Problems:

Write a C++ program to convert a hexadecimal number to its decimal equivalent by processing each hex digit.
Write a C++ program that reads a hexadecimal string and calculates its decimal value using power functions.
Write a C++ program to compute the decimal value of a 32-bit hexadecimal input by iterating over each character.
Write a C++ program that converts a hexadecimal number to decimal using a loop and conditional mapping for digits A-F.

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