Converting Hexadecimal to Decimal.

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

// Function to convert a hexadecimal character to its decimal value
int hexCharToDecimal(char hexChar) {
    if (hexChar >= '0' && hexChar <= '9') {
        return hexChar - '0';  // For characters '0' to '9'
    } else if (hexChar >= 'A' && hexChar <= 'F') {
        return hexChar - 'A' + 10;  // For characters 'A' to 'F'
    } else if (hexChar >= 'a' && hexChar <= 'f') {
        return hexChar - 'a' + 10;  // For lowercase 'a' to 'f'
    }
    return -1;  // Invalid character
}

// Function to convert Hexadecimal to Decimal
int hexadecimalToDecimal(char hex[]) {
    int decimalNumber = 0;
    int length = strlen(hex);  // Find the length of the hex string

    for (int i = 0; i < length; i++) {
        int value = hexCharToDecimal(hex[i]);  // Get decimal value of each hex character
        decimalNumber += value * pow(16, length - i - 1);  // Convert to decimal
    }

    return decimalNumber;
}

int main() {
    char hex[20];

    // Input a hexadecimal number from the user
    printf("Enter a hexadecimal number: ");
    scanf("%s", hex);

    // Convert the hexadecimal number to decimal and display the result
    int decimalNumber = hexadecimalToDecimal(hex);
    printf("Decimal equivalent: %d\n", decimalNumber);

    return 0;
}

Explanation:

Header Files:

• #include <stdio.h>: This is for standard input/output functions like printf() and scanf().
• #include <string.h>: This is for functions that deal with strings, like strlen(), which calculates the length of the hexadecimal input.
• #include <math.h>: This is for the pow() function, which is used to calculate powers of 16.

hexCharToDecimal Function:

• This function takes a single hexadecimal character (e.g., ‘A’, ‘5’) and converts it into its decimal equivalent.
• If the character is a number (0-9), it converts it by subtracting the ASCII value of '0'.
• If the character is a letter (A-F or a-f), it converts it by subtracting the ASCII value of 'A' or 'a', then adding 10.

hexadecimalToDecimal Function:

• This function takes the entire hexadecimal string as input (e.g., “1A3”) and converts it to decimal.
• It starts by calculating the length of the input string.
• It loops through each character of the string, converts each hex digit to its decimal equivalent using hexCharToDecimal(), and calculates the decimal number by multiplying each digit with the appropriate power of 16.

main Function:

• The main function takes a hexadecimal number as input from the user (as a string), calls the hexadecimalToDecimal() function to perform the conversion, and prints the result.

Output:

Input: 1A3

Output:

Enter a hexadecimal number: 1A3
Decimal equivalent: 419

Input: FF

Output:

Enter a hexadecimal number: FF
Decimal equivalent: 255