C program to convert Hexadecimal to Decimal number system

Write a C program to read hexadecimal number from user and convert it to Decimal number system. How to convert from Hexadecimal number system to Decimal number system in C programming. Logic to convert hexadecimal number to decimal number system in C program.



Input hexadecimal: 1A


Decimal number: 26

Required knowledge

Basic C programming, For loop

Hexadecimal number system

Hexadecimal number system is a base 16 number system. It uses 16 symbols to represent all number i.e. 0123456789ABCDEF

Decimal number system

Decimal number system is a base 10 number system. It uses 10 symbols to represent all numbers i.e. 0123456789

Logic to convert Hexadecimal to Decimal

Hexadecimal to decimal conversion

Step by step descriptive logic to convert hexadecimal to decimal number system.

  1. Read any hexadecimal number from user. Store it in some variable hex.
  2. Initialize decimal = 0, digit = length_of_hexadecimal_digit - 1 and i = 0.
  3. Run a loop for each hex digit. Which is the loop structure should look like for(i=0; hex[i]!='\0'; i++).
  4. Inside the loop find the integer value of hex[i]. Store it in some variable say val.
  5. Convert the hex to decimal using decimal = decimal + (val * 16 ^ digit). Where val = hex[i].

Program to convert hexadecimal to decimal

 * C program to convert Hexadecimal to Decimal number system
#include <stdio.h>
#include <math.h>
#include <string.h>

int main()
    char hex[17];
    long long decimal, place;
    int i = 0, val, len;

    decimal = 0;
    place = 1;

     * Input hexadecimal number from user
    printf("Enter any hexadecimal number: ");

    /* Find the length of total number of hex digit */
    len = strlen(hex);

     * Iterate over each hex digit
    for(i=0; hex[i]!='\0'; i++)
         * Find the decimal representation of hex[i]
        if(hex[i]>='0' && hex[i]<='9')
            val = hex[i] - 48;
        else if(hex[i]>='a' && hex[i]<='f')
            val = hex[i] - 97 + 10;
        else if(hex[i]>='A' && hex[i]<='F')
            val = hex[i] - 65 + 10;

        decimal += val * pow(16, len);

    printf("Hexadecimal number = %s\n", hex);
    printf("Decimal number = %lld", decimal);

    return 0;


Enter any hexadecimal number: 1a
Hexadecimal number = 1a
Decimal number = 26

Happy coding 😉

Write your doubts or suggestion. I will try my best to help. You must escape source code before commenting. To format your source code paste your source code inside
<pre><code> ----Your Source Code---- </code></pre>