C Programming Code Examples

C > For Loops and While Loops Code Examples

C program to convert Hexadecimal to Decimal number system

C program to convert Hexadecimal to Decimal number system

Write a C program to input 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.

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

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

#include <stdio.h>
#include <math.h>
#include <string.h>

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

    decimal = 0;
    place = 1;

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

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

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

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

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

    return 0;
}